Concept:A screw gauge measures small dimensions using least count (LC) = pitch / circular scale divisions.
The actual diameter = linear scale reading + (circular scale reading × LC) − zero error.
Explanation:Given: pitch = 0.5 mm, circular scale divisions = 100.
LC =
1000.5​=0.005 mm.
For Wire‑1 (known diameter
0.650 mm):
Linear scale reading (LSR) =
0.5 mm, circular scale reading (CSR) =
42.
Measured reading =
0.5+(42×0.005)=0.5+0.210=0.710 mm.
Zero error = measured − actual =
0.710−0.650=0.060 mm (positive).
For Wire‑2:
LSR =
1.5 mm, CSR =
95.
Measured reading =
1.5+(95×0.005)=1.5+0.475=1.975 mm.
Correct diameter
d = measured − zero error =
1.975−0.060=1.915 mm.
Convert to
μm:
1.915×1000=1915 μm.
Answer:1915\
μm