widely used in education, laboratories, and medical measurements as well as its industrial applications. However, the toxicity of mercury and the risk of spills, through broken glassware, has led to its decline. It is also easier to interface other types of sensor to electronic systems. By 1991 it had mostly been replaced by other technologies. Use as a standard Mercury gauges are commonly used as the primary standard for pressure by national measurement standards laboratories. For instance, the National Institute of Standards and Technology (NIST) in the US uses a gauge that is three metres tall and contains of mercury. For precision, ultrasonics are used to measure the mercury column height. However, in 2019 the backup gauge was decommissioned after being out of service for years. It was so large that it could not be removed by normal means; a hole was cut in the ceiling to extract it. The decommissioning was part of an international move to stop using mercury in standards laboratories for environmental reasons. NIST will eventually also take the main mercury gauge out of service after a portable photonic device is installed to replace it. See also McLeod gauge, a type of mercury pressure gauge used for calibrating electronic pressure gauges References Bibliography COWI Consulting Engineers and Planners, Mercury: A Global Pollutant Requiring Global Initiatives, Nordic Council of Ministers, 2002 . Hála, Eduard; Pick, Jiří; Fried, Vojtěch; Vilím, O.; Standart, George (trans), Vapour–Liquid Equilibrium, Pergamon Press, 1967 (Elsevier reprint, 2013 ). Herman, Irving, Physics of the Human Body, Springer Science & Business Media, 2007 . Kopp, Brian, "Industrial telemetry", ch. 18 in, Telemetry Systems Engineering, Artech House, 2002 . Kotz, John C.; Treichel, Paul M.; Townsend, John R., Chemistry and Chemical Reactivity, vol. 1, Cengage Learning, 2008 . Lechevalier, Hubert A., "The Waksman Institute of Microbiology, 1954 to 1984", The Journal of the Rutgers University, vol. 49–51, pp. 20–45, Associated Friends of the Library of Rutgers University, 1987. Lee, Jennifer Lauren, "No longer under pressure: NIST dismantles giant mercury manometer", NIST, 28 June 2019/15 January 2020, retrieved and archived 29 August 2020. Lindh, Wilburta Q.; Pooler, Marilyn S.; Tamparo, Carol D.; Dahl, Barbara M., Delmar's Clinical Medical Assisting, Cengage Learning, 2009 . Mack, Donald M., Instrumentman 1 & C, United States Government Priniting Office, 1990 (1973 edition ). Purssglove, Thomas Paramore, "Pressure gauge", English Patents of Inventions, Specifications: 1858, 2675-2752, patent no. 2739, filed 1 December