Micrometer (device)
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A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw for accurate measurement of the size of components. It is widely used in mechanical engineering,
Modern micrometer with a reading of 1.639 ± 0.005 mm. Assuming no zero error, this is also the measurement. (One may need to enlarge the image to read it.)
Outside, inside, and depth micrometers. The outside micrometer has a unit conversion chart between fractional and decimal inch measurements etched onto the frame.
Gascoigne's Micrometer, as drawn by Robert Hooke, c. 1668
Another large micrometer in use
Vernier scale
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A vernier scale, named after Pierre Vernier, is a visual aid to take an accurate measurement reading between two graduation markings on a linear scale by using mechanical interpolation, which increase
Micrometer (device)
…analog micrometers, the position of the thimble is read directly from scale markings on the thimble and sleeve (for names of parts see next section). A vernier scale is often included, which allows the position to be read to a fraction of the smallest scale mark. In digital micrometers, an electronic readout displays…
Vernier caliper scales; main at top, vernier at bottom. It reads 3.58 ± 0.02 mm by adding 3.00 mm (left red mark) on the fixed main scale to vernier 0.58 mm (right red mark). The main scale reading is that to the left of the zero on the vernier scale. The vernier reading is found by locating the best aligned lines between the two scales. The 0.02 mm engraving indicates the caliper's readability and is the "vernier constant" for this scale.
Vernier micrometer reading 5.783 ± 0.001 mm, comprising 5.5 mm on main screw lead scale, 0.28 mm on screw rotation scale, and 0.003 mm added from vernier.