Measurement of length:
If the Zeroth division of the head scale does not coincide with the index line the Screw gauge has Zero error.
If the Zeroth division of the head Scale is below the index line of the pitch Scale, the error is said to be +ve and correction is negative. If the Zeroth division of the head scale is above the index line of the pitch scale, the error is said to be -ve and correction is positive. The Diameter of your pencil and a given pin is measured with a screw Gauge.
In some screw gauges, the Zero error can be eliminated by adjusting the position of the stud (S ).
Same units are used for P.S.R. and L.C.
The last column in finding the diameter of a bob in the tabular form is P.S.R + (C.H.S.R X L.C). Vernier Callipers and Screw Guage are Mechanical Devices.
The least count of an ordinary scale is 1 mm.
To hold the marble tightly between S and S , we used by rotating the Milled head M.1