shift output s for shaft 260 is obtained as a measure of relative acceleration between mass 262 and base 264 the above described developments in axial shift compensation and axial shift measurement have been given in respect of transducers utilising the axial in line profile shift response the same principles are applicable to the radial profile shift response fig8 15 which also exhibit the characteristic that the profile shifts in opposite directions relative to the respective sensor assemblies for two transducer regions under a common torque the regions having been magnetised under opposite directions of rotation but that the profile shifts in the same direction relative to the respective sensor assemblies for an axial displacement of the shaft other aspects of the invention arise out of a finding that the use of magnets to magnetise encode a rotating shaft can result in the generation of eddy currents in the shaft an example of this has been found in the magnetisation procedure described above with reference to fig1 3 c one practical way of rotating the shaft relative to a fixed permanent magnet assembly is to mount it in a lathe rotational speeds of 3000 r p m and greater have been used adaptation of ordinary lathe machines for this purpose provides conductive contact with the ends of the shaft and a closed electrical path through the machine what has been found is that on shafts where the axial length of magnetised region is a significant proportion of the shaft length high eddy currents may be set up in the shaft which have any axial component along the shaft which then flows through the external machine path these currents have been measured in the range 10 to greater.