A device for indicating changes in resistance of a living body, the device comprising: a resistance measuring circuit having external leads for sensing the resistance of a living body placed across the external leads; amplifier means for producing an analog measurement signal indicative of the sensed body resistance; a digital processing unit for digitizing and digitally processing themeasurement signal to substantially offset the effects of component aging, tolerances and temperature on the accuracy of the measurement signal; and indicator means responsive to the processed measurement signal for displaying visually perceivable indicia representative of sensed body resistance changes; the digital processing unit including means for substituting a plurality of electrical resistance values for sensing by the amplifier means in lieu of a body resistance, said plurality simulating a plurality of body resistance values; means for digitizing and storing in memory the plurality of measurement signal values corresponding to the plurality of simulated body resistance values; the device further comprising manually positionable means operable by the user to adjust a base value; means for subtracting the adjusted base value from each sampled value to obtain the measurement signal; the device being characterised in that the digital processing unit further includes means to interpolate between the measurement signal values obtained for the simulated body resistance values to quantify the expected measurement signal values for a plurality of additional body resistance values; means for forming and storing a table relating expected measurement signal values for respective body resistance values based upon said interpolation; means for subtracting the monitored body's electrical resistance value from a stored expected measurement signal value that depends on the of the manually adjustable means to produce an adjusted measurement signal as the measurement signal to the indicator means, and sensitivity adjustment means including means for multiplying the processed measurement signal by a gain factor that depends on the position of the manually adjustable means without affecting the operation of the subtracting means, and for applying the result to the indicator means. a resistance measuring circuit having external leads for sensing the resistance of a living body placed across the external leads; amplifier means for producing an analog measurement signal indicative of the sensed body resistance; a digital processing unit for digitizing and digitally processing themeasurement signal to substantially offset the effects of component aging, tolerances and temperature on the accuracy of the measurement signal; and indicator means responsive to the processed measurement signal for displaying visually perceivable indicia representative of sensed body resistance changes; the digital processing unit including means for substituting a plurality of electrical resistance values for sensing by the amplifier means in lieu of a body resistance, said plurality simulating a plurality of body resistance values; means for digitizing and storing in memory the plurality of measurement signal values corresponding to the plurality of simulated body resistance values; the device further comprising manually positionable means operable by the user to adjust a base value; means for subtracting the adjusted base value from each sampled value to obtain the measurement signal; the device being characterised in that the digital processing unit further includes means to interpolate between the measurement signal values obtained for the simulated body resistance values to quantify the expected measurement signal values for a plurality of additional body resistance values; means for forming and storing a table relating expected measurement signal values for respective body resistance values based upon said interpolation; means for subtracting the monitored body's electrical resistance value from a stored expected measurement signal value that depends on the of the manually adjustable means to produce an adjusted measurement signal as the measurement signal to the indicator means, and sensitivity adjustment means including means for multiplying the processed measurement signal by a gain factor that depends on the position of the manually adjustable means without affecting the operation of the subtracting means, and for applying the result to the indicator means.