Fig 1Vernier callipers and screw gaugeDrag to turn · pinch or scroll to zoomMSR 19 mm · VSR 0.6 mm · reading 19.6 mm · zero error 0.0 mm · corrected 19.6 mm
The reading, beside the scaleSteel vernier calliper, least count 0.1 mmScrew gauge, least count 0.01 mmVernier: 10 vernier divisions span 9 main-scale millimetres, so each is 0.1 mm shorter; the vernier line that lines up exactly with a main-scale mark gives the tenths. Reading = main scale reading + coinciding division × 0.1 mm. Screw gauge: one turn of the head moves the screw one pitch (0.5 mm) and the head has 50 divisions, so each is 0.01 mm. Reading = linear scale + circular scale division × 0.01 mm. Close the jaws first: a zero error is subtracted with its sign.