The least count (L.C.) of a screw gauge is the linear distance moved by its screw along the main scale when the circular scale is rotated by one division on it.
L.C=Pitch of screw gaugeTotal number of divisions on circular scale
If pitch of a screw gauge is 1mm and the circular scale has 100 divisions, then
L.C = 1 mm100=0.01 mm=0.001 cm