An electronic apparatus for reducing interference in a desired 
signal, the apparatus comprising: (a) a plurality of measurement 
signal lines, each connected to a respective measurement 
signal electrode; and (b) one or more reference 
signal lines, each connected to respective one or more reference electrodes; each of said measurement 
signal lines or a respective group of said measurement 
signal lines being associated by being in close physical proximity with a respective one of said reference signal lines for a substantial part of their lengths, so that each measurement signal line or signal line group with its corresponding reference signal line forms a measurement signal line or measurement signal line group / reference signal 
line pair, said electronic apparatus further comprising subtraction means for subtracting an interference on each reference signal line from an interference 
signal on the associated measurement signal line or from each measurement signal line in the measurement signal line group in that measurement signal line or measurement signal line group / reference signal 
line pair, wherein at least one of the measurement signal electrodes is arranged to be in direct 
electrical connection with a subject and at least one of the reference signal electrodes is arranged to be in close physical proximity but not in direct electrical contact with the subject.