Screw Gaugues

There are two scales
: 1.Main scale, graduated along the axis of the screw. 
2.Cap scale/Head scale (H). 

PRINCIPLE: The linear distance moved by the screw head is directly proportional to the amount of rotation given to the screw. 
 Distance moved on sleeve by screw, after giving one complete revolution is called Pitch.
  Let there be ‘N’ divisions on circular scale and on ‘n’ complete rotations screw shifts by one sleeve unit, then Least Count can be given by 1/(n*N). 


Thus reading of micrometer can be given by 
M.S. reading + (C.S. reading*L.C.) 

When Spindle touches Anvil, indicator of ‘0’ on circular scale should touch the main scale line at ‘0’. If this doesn’t happen, we call it error (positive/negative). 

If the Thimble is yet to reach ‘0’ on main scale, it is positive error and if it has passed that point, it is negative error. Correction is made to satisfy error. 

ONE SMALL QUESTION FOR U drop ur answers in the comment box

 What is the reading of this micrometer? Given that there are 50 divisions on circular scale. *What if the zero error is -0.25?