A micrometer (or micrometre) is by definition 1×10−6 of a metre (SI Standard prefix “micro” = 10−6); that is, one-millionth of a metre (or one-thousandth of a millimetre, 0.001 mm, or about 0.000039 inches). Its unit symbol in the International System of Units (SI) is µm. The latter may be rendered as um if Greek fonts are not available or not admissible. “Micron” comes from Ancient Greek: μικρόν mikrón, which means “small”.
The term micron and the symbol µ, representing the micrometre, were officially accepted between 1879 and 1967, but officially revoked by the ISI in 1967. Nevertheless, in practice, “micron” remains a widely used term in preference to “micrometre” in many English-speaking countries, and in American English the use of “micron” helps differentiate the unit from the micrometer, a measuring device, because the unit’s name in mainstream American spelling is a homograph of the device’s name. The term “micron” has particular currency in science and is extensively used in most English-speaking countries in the fields of geology, biology, physics, astronomy, machining, and the semiconductor industry.
A micrometer is a common unit of measurement for wavelengths of infrared radiation.
The micrometer is a precision measuring instrument, used by engineers. Each revolution of the rachet moves the spindle face 0.5mm towards the anvil face. The object to be measured is placed between the anvil face and the spindle face. The rachet is turned clockwise until the object is ‘trapped’ between these two surfaces and the rachet makes a ‘clicking’ noise. This means that the rachet cannot be tightened anymore and the measurement can be read.
How to measure reading?
1. Read the scale on the sleeve. The example clearly shows12 mm divisions.
2. Still reading the scale on the sleeve, a further ½ mm (0.5) measurement can be seen in the bottom half of the scale. The measurement now reads 12.5mm.
3. Finally, the thimble scale shows 16 full divisions (these are hundredths of a mm).
The final measurement is 12.5mm + 0.16mm = 12.66
The least count of micrometer is 0.01mm or 0.001 cm.