Editing Pressure measurement (section)

===Spinning-rotor gauge===
The spinning-rotor gauge works by measuring how a rotating ball is slowed by the viscosity of the gas being measured. The ball is made of steel and is magnetically levitated inside a steel tube closed at one end and exposed to the gas to be measured at the other. The ball is brought up to speed (about 2500 or 3800&nbsp;[[radian|rad]]/s), and the deceleration rate is measured after switching off the drive, by electromagnetic transducers.<ref>A. Chambers, ''Basic Vacuum Technology'', pp. 100–102, CRC Press, 1998. {{ISBN|0585254915}}.</ref> The range of the instrument is 5<sup>−5</sup> to 10<sup>2</sup>&nbsp;Pa (10<sup>3</sup>&nbsp;Pa with less accuracy). It is accurate and stable enough to be used as a [[secondary standard]]. During the last years this type of gauge became much more user friendly and easier to operate. In the past the instrument was famous for requiring some skill and knowledge to use correctly. For high accuracy measurements various corrections must be applied and the ball must be spun at a pressure well below the intended measurement pressure for five hours before using. It is most useful in calibration and research laboratories where high accuracy is required and qualified technicians are available.<ref>John F. O'Hanlon, ''A User's Guide to Vacuum Technology'', pp. 92–94, John Wiley & Sons, 2005. {{ISBN|0471467154}}.</ref> Insulation vacuum monitoring of cryogenic liquids is a well suited application for this system too. With the inexpensive and long term stable, weldable sensor, that can be separated from the more costly electronics, it is a perfect fit to all static vacuums.