44results about How to "Efficient measurement" patented technology

In a measurement processing apparatus for measuring a geometric feature of an object image: a measurement-reference-element setting unit automatically sets at least one first measurement reference element for use in measurement of the geometric feature of the object image, at at least one first position on the object image based on first image data representing the object image and position information indicating at least one second position of at least one second measurement reference element which is set on a measurement reference image corresponding to the object image; and a geometric-feature measurement unit measures the geometric feature of the object image based on the at least one first position of the at least one first measurement reference element.

The application discloses a kind of SF6 density relay comprehensive calibration instrument and calibration and measurement method, including intermediate pipeline and be located on the air pump of intermediate pipeline, the one end of the intermediate pipeline is respectively communicated with the one end of safety valve pipeline, first pipeline one end, second pipeline one end, the other end of intermediate pipeline is respectively communicated with the one end of micro water measuring pipeline and third pipeline one end, the other end of the micro water measuring pipeline is respectively communicated with the one end of inlet pipeline and purity measuring pipeline, the other end of third pipeline is respectively communicated with the other end of first pipeline and fourth pipeline one end, the other end of the fourth pipeline is respectively communicated with the other end of purity measuring pipeline, the other end of second pipeline and muffler pipeline, intermediate pipeline side is equipped with suction pipeline;The application has adopted new pneumatic circuit design, combines density relay system calibration circuit with moisture measurement circuit and purity measurement circuit together, with the characteristics such as high measurement efficiency, convenient, its loop structure is simplified, and measurement is efficient.

The utility model relates to the technical field of stocker cargo carrying tables, and discloses a sensor mounting structure of a stocker cargo carrying table, which comprises a cargo carrying table main body, a first aluminum alloy beam is fixedly mounted on the left side of the cargo carrying table main body, and a second aluminum alloy beam is fixedly mounted on the right side of the cargo carrying table main body; the code scanner is fixedly mounted on the back surface of the cargo carrying table main body; and the camera support is fixedly installed on the top of the second aluminum alloy beam, and a camera is fixedly installed on the inner wall of the camera support. According to the utility model, through the design of the sensor layout mechanism and the cooperation of the groove-shaped photoelectricity and the limit switch, compared with the common diffuse reflection photoelectricity, the groove-shaped photoelectricity has the advantages of strong anti-interference capability, various specifications and styles, higher intelligence and higher reliability due to the special structural design, and compared with the existing scheme, the limit switch has the advantages that the structure is simple and the cost is low. And in the aspect of emergency braking treatment, braking treatment is quicker and more efficient, so that the safety can be further improved.

The application provides a device for compressor blade length size three-coordinate detection, which comprises a plurality of compressor blade clamping units arranged in a matrix mode, and each compressor blade clamping unit mainly comprises positioning round pins, sliding U-shaped pressing blocks and U-shaped positioning limiting blocks. The three positioning round pins are arranged in parallel, one end of the positioning round pin comprises a spherical surface for supporting a side end surface of a compressor blade edge plate blade body; the sliding U-shaped pressing block comprises a first U-shaped notch for pressing a circumferential corner of the compressor blade edge plate; the U-shaped positioning limiting block comprises a second U-shaped notch for pressing the circumferential corner of the compressor blade edge plate; and the spacing between the sliding U-shaped pressing block and the U-shaped positioning limiting block is variable. The device can realize three-coordinate detection of multiple blades clamped at one time, improves the measurement efficiency and reduces the labor intensity of the inspectors.

The utility model relates to photovoltaic equipment installation technical field discloses an auxiliary measuring tool for photovoltaic installation, including measuring scale, the upper surface of measuring scale is inlayed and is equipped with horizontal bubble disc, the bottom of measuring scale is equipped with three screw thread support legs of triangle distribution, the bottom of screw thread support leg outer surface is connected with internal thread support foot through screw thread adaptation, the middle part of measuring scale upper surface is printed with scale mark along its length direction. This auxiliary measuring tool for photovoltaic installation, through setting up the combination structure of horizontal bubble disc, three screw thread support legs of triangle distribution and internal thread support foot, can quickly adjust the horizontal state of the tool, and horizontal bubble disc can intuitively feedback the inclination, and the triangle distribution of three support legs has stable supporting property, and cooperates the internal thread support foot of screw thread adjustment, can flexibly adapt the installation ground of different flatness, ensures the horizontal accuracy of the measurement datum plane, and provides reliable foundation for subsequent length, angle measurement.

The invention belongs to the technical field of aero-engines, and discloses a turbine casing impact heat exchange test method and system, and the method comprises the steps: determining impact hole parameter research variables, and the structure parameters and number of aperture replacement parts, and adjusting the diameters of impact holes through the aperture replacement parts; the number and arrangement of the impact holes are adjusted by installing hole diameter replacement parts and a plurality of plugs on the impact hole plates; the impact target distance is adjusted through different numbers of target distance replacement parts; and performing an impact cooling heat exchange test on each combined cartridge receiver impact heat exchange test piece to obtain heat exchange coefficients of impact target surfaces of different research variables. The hole diameter replacement part is arranged to change the hole diameter and hole arrangement, the target distance replacement part is arranged to change the impact distance, the number of test pieces can be reduced, the machining cost is reduced, the machining period is shortened, meanwhile, disassembly and assembly are easy, disassembly and assembly time is short, test consistency is guaranteed, effective measurement of the impact heat exchange test temperature is achieved, and therefore the corresponding impact heat exchange coefficient is obtained.

The invention provides automatic measuring equipment for a medium-length hole in a mine, and relates to the technical field. Comprising a frame, a plurality of measuring rods and an unwinding device, a limiting device is further arranged at the bottom of the frame, a transfer locking device is arranged between the limiting device and the unwinding device, the transfer locking device comprises a vertically-arranged driving shaft, and a positioning rod is fixed to the side wall of the driving shaft; the tail ends of the positioning rods are provided with positioning assemblies used for grabbing the measuring rods, the positioning assemblies directionally deflect around the driving shaft, the unwinding device comprises an unwinding roller and a rope, the bottom of the unwinding roller is fixedly connected with the first measuring rod, the unwinding roller is located on the deflection path of the positioning assemblies, and the rope is arranged on the unwinding roller. The positioning assembly at least comprises three locking rollers, and the multiple locking rollers are arranged in a C shape. The equipment can achieve automatic sleeving and fixing of the multiple measuring rods, and rapid and efficient measurement of deep holes in mines is achieved.

This invention proposes an apparatus and method for measuring the stress distribution of a KDP crystal structure. The apparatus includes: a laser, a convex lens, a first linear polarizer, a crystal sample to be tested, a vertical lifting stage, a horizontal displacement stage, a second linear polarizer, a CCD image sensor, a screen, and a computer. The laser, convex lens, first linear polarizer, crystal sample to be tested, second linear polarizer, and screen are arranged sequentially according to the optical path. The crystal sample to be tested is placed on the vertical lifting stage, which is placed on the horizontal displacement stage. The crystal sample to be tested is a Z-cut, double-sided polished KDP crystal. The CCD image sensor is connected to the computer. This apparatus and method are used to measure the stress distribution of a Z-cut KDP crystal structure. It is simple, low-cost, has no requirements on sample quality, size, or shape, and has wide adaptability. It can quickly, effectively, accurately, and quantitatively measure the structural stress and stress distribution within the crystal.

The utility model discloses a transformer sound level measurement auxiliary device, which comprises a plurality of sound level probes used for acquiring sound signals of a transformer, and further comprises a probe bearing frame covering the periphery of the transformer, and the plurality of sound level probes are arranged along the circumferential direction of the probe bearing frame. The sound level probes are located on the same horizontal plane, and the distances from the sound level probes to the outer surface of the transformer are equal. According to the utility model, the problem of inconsistent measurement distances caused by positioning deviation in traditional manual measurement is effectively solved, and the accuracy and reliability of measurement data are ensured; secondly, the sound level meter does not need to be held manually or the position of the measuring head does not need to be adjusted frequently, the electric shock safety risk possibly faced by manual operation under the electrified working condition is greatly reduced, and the personal safety of operators is guaranteed; and multiple measuring points can be measured at the same time, so that the condition of long time consumption of a single test caused by manual switching measurement of multiple measuring points in the prior art is changed, and the detection efficiency is greatly improved.

The invention provides a water diversion shaft guide hole excavation precision measuring system which comprises a measuring machine body, the measuring machine body is supported by a mounting table and a fixing mechanism, and an angle adjusting mechanism is arranged between the measuring machine body and the mounting table; the fixing mechanism comprises a plurality of racks connected to the lower side of the mounting table, a supporting plate, a clamping block and a sharp corner brace, a supporting column is fixed to the center of the bottom of the mounting table and slidably sleeved with a mounting sleeve, a plurality of connecting pieces are horizontally connected to the peripheral side of the mounting sleeve, supporting rods are slidably sleeved with the connecting pieces, and one ends of the supporting rods are fixedly connected to the racks; the supporting plate is inserted into the rack in a sliding mode and connected and fixed through a clamping block and a bolt, and a sharp corner brace making contact with the ground is arranged at the bottom of the supporting plate. The device has the advantages of being excellent in stability performance, good in fixing effect, convenient to accurately adjust the angle and efficient in measurement.

The utility model belongs to the technical field of die depth measuring equipment, and particularly relates to a special device for measuring the depth of a die, which comprises a base, a die body arranged on the upper surface of the base, a crossing support arranged on the upper surface of the die body, a ruler needle inserted into the crossing support, and a height gauge arranged at the top end of the ruler needle. A connecting rod is fixedly connected to the top end of the height gauge, and a bolt is transversely connected into the mold body in a threaded mode. According to the utility model, through the arrangement of the height gauge and the crossing support, the depth of a single die can be measured more effectively and more accurately, the crossing support can be firmly supported on the two sides of the die cavity of the die, the problems of unstable single-side support and large fluctuation of measured data caused by the use of a height caliper for measurement in the early stage are avoided, and the two end planes of the crossing support are not easy to fall off. The tool needs to be made into a plane as much as possible, so that the tool can be better combined with supporting positions at the two ends of the die cavity without gaps, errors caused by the gaps are reduced, and the tool is simpler and more convenient, easy to operate, more accurate in data and small in error.

The gas sensor device comprises an emission light source, a first photosensitive sensor and a second photosensitive sensor, the first photosensitive sensor is arranged below and / or above a light path where light emitted by the emission light source is located, and the second photosensitive sensor is arranged on the side, close to the emission light source, of the first photosensitive sensor. The first photosensitive sensor comprises a rear end close to the emission light source and a front end away from the emission light source, the foremost end of the second photosensitive sensor does not exceed the rear end of the first photosensitive sensor, and the plane where the second photosensitive sensor is located intersects with the plane where the first photosensitive sensor is located. Light emitted by the emission light source irradiates the to-be-detected gas, particulate matters in the to-be-detected gas are scattered to generate scattered light, the scattered light below and / or above the particulate matters is received by the first photosensitive sensor, and the scattered light on one side, close to the emission light source, of the particulate matters is received by the second photosensitive sensor, so that the particulate matters in the to-be-detected gas are detected.

The application provides a plane constraint-based spectral confocal probe pose calibration method and device, and belongs to the field of precision measurement and instrument technology.The method comprises the following steps: firstly, at least three non-coplanar plane standard parts are measured by using a contact probe, and through coordinate conversion and fitting, equations of the standard planes in a machine coordinate system are accurately established; then, the same plane parts are measured by using a spectral confocal probe, and the obtained measurement point coordinates and distance values are combined with the known plane equations to construct a linear over-determined equation set about the probe pose parameters (including an optical axis direction vector and a space position vector); finally, the equation set is solved by using a least square method to obtain accurate pose parameters.The application converts a nonlinear problem into a linear solution, avoids iterative calculation, and significantly improves the calibration efficiency and accuracy.Meanwhile, the use of plane constraint allows the measurement points to be uniformly distributed, effectively reduces the equation set ill-conditioning, and enhances the robustness of the calibration process.

The application provides a device and method for fine measurement of a composite propeller blade deformation field. The device comprises an adjustable height horizontal control console, a horizontal plate, a blade loading point fixing device, a plurality of adjustable length displacement calibration probes, an electronic vernier caliper and a base device, and the like. The measurement method provided by the application realizes fine measurement of the blade deformation field of a composite propeller, can accurately, stably, efficiently and at low cost measure the small deformation amplitude of the composite propeller, thereby providing accurate test data support for simulation calculation, and can be applied to deformation measurement of composite propellers of different types and different scales.

The application relates to the technical field of vehicle collision test, and discloses a dynamic displacement measurement system based on inertial navigation technology in vehicle collision test, which comprises an inertial measurement unit, a vehicle-mounted recording unit and a ground control unit; the inertial measurement unit comprises a plurality of sub-inertial navigation units; the sub-inertial navigation units are used for collecting basic operation information of to-be-measured points; the vehicle-mounted recording unit comprises a main inertial navigation unit and a collection and storage module; the main inertial navigation unit is used for collecting main body operation information of a vehicle; the collection and storage module is used for storing information data collected by the main inertial navigation unit and the sub-inertial navigation units; the ground control unit comprises a data processing module; the data processing module is used for processing information data of the main inertial navigation unit and the sub-inertial navigation units, calculating dynamic displacement data of the to-be-measured points, and generating corresponding displacement pictures and reports; when processing the information data of the main inertial navigation unit and the sub-inertial navigation units, the data processing module adopts an inertial navigation algorithm to calculate the dynamic displacement data. The application has a simple structure and can accurately and efficiently complete dynamic displacement measurement of the to-be-measured points.

This invention discloses an experimental method for measuring the electron-hole recombination emission rate. The apparatus for this method includes a laser chip (with an anti-reflection coating on only one end of its horizontal two-sided end face), a plano-convex lens, a polarizer, a fiber optic coupler, an optical fiber, and a spectrometer. The plano-convex lens, polarizer, plano-convex lens, and fiber optic coupler are placed sequentially on the same horizontal line on both sides of the chip. The fiber optic coupler is connected to the spectrometer via an optical fiber. First, energy is applied to the laser chip, causing it to emit light from both sides. The spectra from both sides are focused onto the fiber optic coupler by the plano-convex lens and then transmitted to the spectrometer via the optical fiber. By rotating the polarizer, different polarization spectra can be selected to obtain specific spectral images under transverse electric / magnetic field modes. Finally, by substituting the spectral data from both ends into the established formula, the electron-hole recombination rate of the laser chip can be calculated.

The present invention relates to a method of measuring particles present in a solution. A particle measuring device according to the present invention, wherein, including: a power supply unit for applying a voltage; a chip formed with a plurality of electrodes arranged in order on a micro flow path through which a fluid passes; a circuit unit in which at least a portion of a bridge circuit in which a plurality of electrodes formed on the chip form a predetermined electrical state is printed; and a measurement unit, the power supply unit applies a voltage to the circuit unit, the measurement unit for measuring changes in the output signal of the bridge circuit due to particles in the fluid passing through the micro flow path. According to the present invention, the change in the electrical signal can be accurately measured using the change in the electrical signal in the solution, and the size and time of the change in the electrical signal can be accurately measured using the change in the electrical signal.

The application discloses a wide-range air leakage amount detection device containing micro-flow measurement and relates to the technical field of air leakage amount detection.The wide-range air leakage amount detection device comprises an air flow measurement device and an automatic stable pressure ventilator, the air outlet of the air flow measurement device is connected with the air inlet of the automatic stable pressure ventilator, the air flow measurement device comprises a measurement pipeline, the inside of the measurement pipeline is provided with small nozzles, middle nozzles and large nozzles which are sequentially sleeved, the large nozzles are fixed in the inside of the measurement pipeline, the small nozzles and the middle nozzles are both slidably arranged in the inside of the measurement pipeline and are driven to slide by a driving mechanism for changing the gas flow cross section of the measurement pipeline.The wide-range air leakage amount detection device can cover all air leakage amount grades stipulated by new regulations and all air leakage amount grades stipulated by air valve standards, the detection conclusion is objective and fair, and the detection efficiency is high.

This utility model relates to the field of medical device technology, and in particular to a device for measuring cervical spine data in a head-down posture. The device includes a first sliding scale, a second sliding scale, and a head-limiting component. The first sliding scale includes a first sliding component and a first sliding main scale, and the second sliding scale includes a second sliding component and a second sliding main scale. The first sliding component is connected to the head-limiting component, and the first sliding main scale and the second sliding component are connected. The first and second sliding scales are arranged in a perpendicular and orthogonal spatial layout. The first sliding main scale is used to measure the lateral cervical spine data of the user from an upright posture to a head-down posture; the second sliding main scale is used to measure the longitudinal cervical spine data of the user from an upright posture to a head-down posture; the head-limiting component is used to restrict the rotation of the user's head. The above technical solution can accurately measure the cervical spine data of the user in a head-down posture.

This invention discloses a relay-type large strain monitoring steel strand and its manufacturing and usage methods. It is applicable to large strain monitoring of various types of steel strand components in civil engineering. By embedding corresponding fiber optic strain sensing fibers in grooves corresponding to the relaxed and tensioned states of irregularly shaped steel wires, applying adhesive and wrapping with a sheath for fixation, and then twisting them with edge wires to form a steel strand, it is possible to achieve quasi-distributed dense monitoring of large strain along the entire length of the strand itself. The strain monitoring range at each point is up to 8000με, which solves the problem of difficult monitoring of large strain along the prestressed steel strand in concrete structures. In addition, the segmented relay-type large strain monitoring steel strand structure based on weak grating sensing has its own fiber optic lead, which is convenient and quick to use and easy to promote and apply.

The application discloses a double-array resistivity hole pressure static sounding device, which comprises a conical probe, a hole pressure filter ring, a sidewall upper friction cylinder, a resistivity testing module, a digital circuit board and an analog-digital converter; the conical probe is connected with the sidewall upper friction cylinder through the hole pressure filter ring; the sidewall upper friction cylinder is connected with the resistivity testing module; the sidewall upper friction cylinder is internally provided with a hole pressure sensor, a cone tip resistance sensor, a side friction resistance sensor, a temperature compensator and an inclinometer which are connected with the digital circuit board; the digital circuit board is connected with the resistivity testing module; the digital circuit board is connected with the analog-digital converter through a coaxial cable; the coaxial cable is connected with the analog-digital converter and a data acquisition instrument outside the device; the soil body horizontal resistivity measured by the application has the characteristics of in-situ, rapid, continuous and reliable, and provides a powerful detection tool for geotechnical engineering practice.

The application discloses a kind of based on self-interference's spatiotemporal focusing femtosecond laser pulse front skew measurement device and method.For the measurement light path complex problem that traditional method needs to provide reference light without pulse front skew in spatiotemporal focusing pulse front skew measurement by compressor, self-interference method is proposed to simplify light path, by splitting the light to be measured, reference light opposite to the skew direction of the pulse to be measured is directly generated, so that interference measurement is realized.Through the linear relationship between the center position of interference fringe and the delay difference between beams, the pulse front skew can be directly obtained.The device provides a simple and reliable pulse spatiotemporal characteristic analysis scheme for application in large-aperture high-power devices and implementation of spatiotemporal focusing pulse front skew measurement at focal point.

This invention discloses a nuclear magnetic resonance (NMR) method for measuring the solid phase deposition of crude oil in porous media, belonging to the field of oil and gas reservoir development technology. By using a single saturation of crude oil in a core sample and leveraging the characteristics of online NMR technology, the method employs a comparison of experimental and NMR measurements, along with a 1:1 standard line reference, to determine the standard echo interval T in the transverse relaxation time T2 measurement acquisition parameters. E This method directly measures the amount of solid phase deposition in pore fluids in situ, solving the technical problems of existing technologies that cannot maintain the original characteristics of the sample, effectively avoid the interference of solid skeleton response and solid phase deposition particles, and are difficult to measure the solid phase deposition content of active oil in situ. It achieves the technical effect of rapid, efficient and accurate measurement of the amount of crude oil solid phase precipitation in cores under specific temperature and pressure conditions. The method is reliable in principle, simple to operate and highly applicable, and the test results are accurate and reliable, making it more suitable for the fine characterization needs of complex oil and gas reservoirs.

The application relates to the technical field of eddy current sensors and voltage calibration. The eddy current sensor calibration method for small-diameter metal balls comprises four parts of coordinate system establishment, calibration data acquisition, calibration sample set construction and calibration equation coefficient optimization. Through innovative coordinate system definition and position parameterization, combined with an intelligent optimization algorithm, the application successfully establishes an accurate voltage-position relationship model capable of accurately representing the small-diameter metal ball center deviating from the actual effective measurement axis of the sensor, and effectively compensates for the nonlinear measurement error caused by the ball center eccentricity, surface high curvature and sensor axis deviation.

The application relates to the technical field of measurement, in particular to an intelligent measurement method and device based on urban planning and architectural design. The method comprises the following steps: setting a flight route of a flying device, a target scanning area and a scanning position. Then, according to the measurement characteristics of a target measurement object in the target scanning area, a target wave band is selected from preset wave bands as a scanning wave band of a sub-area; the sub-area in the scanning range of the flying device at each scanning position is grouped, the sub-area is scanned according to the corresponding scanning wave band of each group, and point cloud data is acquired; the actual point cloud quantity in each grid space after fusion is compared with a standard point cloud quantity, the flight route of the flying device and the actual point cloud data are adjusted according to the comparison result; and a three-dimensional model is constructed according to the adjusted point cloud data and corresponding image data. The application solves the problem of low measurement precision and realizes efficient and accurate measurement of a target measurement area.

The utility model provides a digital high-precision standard thermometer, which comprises a digital thermometer body, an arc-shaped groove is arranged at the end part of the digital thermometer body, and a heat conduction part is arranged on the inner wall of the arc-shaped groove; a fixing hoop is arranged at the end part of the arc-shaped groove, and the fixing hoop is detachably mounted at the end part of the arc-shaped groove through a fastener; a clamping groove is formed between the fixing hoop and the arc-shaped groove. When the digital thermometer is used, the arc-shaped groove is formed in the end of the digital thermometer body, the heat conduction part is arranged in the arc-shaped groove, the heat conduction part is attached to the outer surface of a pipeline, and meanwhile the digital thermometer body is fixed to the pipeline through cooperation of the fixing hoop and the arc-shaped groove. Therefore, the temperature of the outer surface of the pipeline can be directly monitored, and the digital thermometer body can be conveniently fixed on the outer surface of the pipeline.

The application belongs to the field of riverway detection equipment, and discloses a riverway section size detection device, which comprises a vehicle frame, a plurality of rollers fixed below the vehicle frame, a plurality of fixing devices arranged on the two sides of the upper portion of the vehicle frame, a placing device fixed at one end of the upper portion of the vehicle frame, a transmission device fixed on the upper portion of the vehicle frame, a clamping box fixed at one end of the transmission device, a standard section movably arranged in the transmission device, a starting section connected to one end of the standard section, a moving device movably arranged on the upper portion of the standard section and the starting section, and a measuring device movably arranged on one side of the moving device. The application solves the problems of low efficiency, poor precision, complicated operation and weak adaptability of the prior art riverway section size detection method and device, realizes rapid, accurate and efficient measurement of the riverway section size, meets the measurement requirements in different riverway environments, and is suitable for riverway detection.

This invention relates to the field of precision measuring instruments, and discloses a high-precision roller spherical base surface measuring device and method. The high-precision roller spherical base surface measuring device includes: a measuring instrument body, a measuring head mounted on the measuring instrument body, a clamping mechanism, an identification measuring mechanism, and a control terminal; the clamping mechanism includes: a clamping component, a rotation drive component, and a pre-support component. The clamping component is mainly used to clamp the roller to be measured, and the rotation drive component is connected to the clamping component, mainly used to drive the clamped roller to rotate around a theoretical axis. This invention automatically identifies the roller size and determines the optimal clamping parameters through machine vision, and combines three-dimensional scanning to calibrate the clamping posture in real time. It can dynamically generate an adaptive measurement path based on the measured deviation, effectively solving the system error problem caused by inconsistent clamping in traditional measurements, significantly shortening the measurement time for a single piece, and achieving efficient and reliable measurement of the tapered roller spherical base surface with micron-level accuracy.

This application discloses a method, apparatus, ultrasound device, and storage medium for detecting cardiac ultrasound data. The method includes: acquiring cardiac ultrasound data to be detected; extracting image features from the cardiac ultrasound data and determining the target section type corresponding to the cardiac ultrasound data based on the image features; when the target section type is a parasternal left ventricular long-axis section, determining the target section image for display from the cardiac ultrasound data; determining the diameter data of the left ventricular outflow channel along the parasternal left ventricular long axis from the target section image, and associating the diameter data with the target section image for display. By determining the section type of the cardiac ultrasound data, and when the section type is a parasternal left ventricular long-axis section, directly extracting the target section image for display from the cardiac ultrasound data, this application ensures effective subsequent measurement of the left ventricular outflow channel, obtaining data on the left ventricular outflow channel, and improving measurement accuracy.