Which instrument is this and what is its use

What is the use of this instrument


Spindle micrometer. we can use this on vibration probe cross checking time… At first we place the vibration probe tip very close( almost touch with that plate which is in front of spindle micrometer) to that micrometer…that time we get 0vdc on multimeter… Once we started to increase the gap between probe and that flat surface. The voltage would increase parallely. For 10mills we get -2vdc, 50mills we get -10vdc and for 100mills we get almost -18vdc. By using this spindle micrometer we can check the probe linearity.