In a screw gauge, the zero of the circular scale lies 3 divisions above the horizontal pitch line wh

Question

In a screw gauge, the zero of the circular scale lies 3 divisions above the horizontal pitch line when their metallic studs are brought in contact. Using this instrument thickness of a sheet is measured. If pitch scale reading is 1 mm and the circular scale reading is 51 then the correct thickness of the sheet is $\_\_\_\_$ mm . [Assume least count is 0.01 mm ]

Professor PC Thomas Classes · Answer

Since the zero of the circular scale lies above the reference line, the screw gauge has a negative zero error. Zero Error = $-3 	imes 	ext{Least Count} = -3 	imes 0.01 	ext{ mm} = -0.03 	ext{ mm}$. The measured reading is $PR + (CR 	imes LC) = 1 	ext{ mm} + (51 	imes 0.01) 	ext{ mm} = 1.51 	ext{ mm}$. The correct thickness is given by Measured Reading $-$ Zero Error $= 1.51 	ext{ mm} - (-0.03 	ext{ mm}) = 1.54 	ext{ mm}$.