Hysteresis is also another parameter that is useful to measure, particularly in liquid level measurement. It is simply the ratio of the drop-out and the pull-in, usually measured as a percent (%) or decimal. For example a reed switch that has a pull-in distance of 12mm divided by the drop-out of 20mm will have a hysteresis value of 60%. In a level sensor application, such as in a fuel tank in which the liquid reservoir will undergo some movement, a higher hysteresis will ensure that the reed switch does not accidentally activate and provide inaccurate liquid levels.