Physics · Units And Measurements · NEET
No. Pitch is the bigger number: it is how far the screw moves forward in ONE full turn (usually 0.5 mm or 1 mm). Least count is much smaller: it is the pitch divided by the number of divisions on the circular scale. Example: pitch = 0.5 mm and 50 divisions gives LC = 0.5/50 = 0.01 mm. So LC is always smaller than pitch.
Turn the formula around. LC = Pitch / N, so Pitch = LC x N, where N is the number of circular scale divisions. If LC = 0.01 mm and N = 50, then Pitch = 0.01 x 50 = 0.5 mm. NEET 2020 asked exactly this, so learn both directions of the formula.
MSR (Main Scale Reading) is the value on the straight sleeve scale you can see just before the thimble edge, read in mm. CSR (Circular Scale Reading) is the division number on the round thimble that lines up with the main scale reference line. Final reading = MSR + (CSR x LC).
A vernier caliper has LC = 0.01 cm = 0.1 mm. A screw gauge has LC = 0.001 cm = 0.01 mm, which is 10 times finer. This is because the screw turns many times over a small distance, magnifying tiny movements onto a large circular scale. So use a screw gauge for wire or sheet thickness, and a vernier for slightly bigger objects.
Not in the basic reading. First get MSR + CSR x LC. Then correct for zero error separately: corrected reading = observed reading minus zero error (keep the sign). Zero error is a whole separate topic covered next; for pitch and least count, focus only on MSR + CSR x LC.
A screw gauge has least count of 0.01 mm and there are 50 divisions in its circular scale. The pitch of the screw gauge is:
A screw gauge gives the following readings when measuring the diameter of a wire: Main scale reading = 0 mm; Circular scale reading = 52 divisions. 1 mm on the main scale corresponds to 100 divisions on the circular scale. The diameter of the wire is:
A student measured the diameter of a small steel ball using a screw gauge of least count 0.001 cm. The main scale reading is 5 mm and zero of the circular scale coincides with 25 divisions above the reference level. If the screw gauge has a zero error of -0.004 cm, the correct diameter of the ball is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Least Count = Pitch / (number of divisions on the circular scale). Example: pitch 0.5 mm with 50 divisions gives LC = 0.5/50 = 0.01 mm = 0.001 cm.
Pitch is the distance the screw (thimble) advances along the main scale in one complete rotation. For a standard NEET screw gauge it is usually 0.5 mm or 1 mm. Pitch = distance moved / number of full rotations.
Reading = Main Scale Reading (MSR, in mm) + (Circular Scale Reading x Least Count). Then subtract the zero error, keeping its sign, to get the true measurement.
Most NEET problems use LC = 0.01 mm = 0.001 cm. This is 10 times finer than a vernier caliper (0.1 mm), which is why the screw gauge is used for very thin wires and sheets.
The screw converts a small forward motion into a large rotation of the circular scale, so a tiny movement spreads across many divisions. This gives LC = 0.01 mm versus 0.1 mm for a vernier, making the screw gauge ten times more precise.
