Hysteresis for reed sensors can be selected. This is particularly important if one is measuring the level of a fluid in a moving vehicle. A hysteresis of around 50% would be ideal. Here, once a low level, say of brake fluid is detected, the reed sensor will activate a light a light on the dashboard. With a 50% differential the light will remain on and steady. If the hysteresis was in the 90% range, the dashboard light would be constantly going on and off as the brake fluid slashed around with each bump or curve in the road. Hall sensors have no hysteresis. They have a gradual ‘ON’ signal and a gradual ‘OFF’ signal. Electromechanical sensors have a fixed hysteresis that cannot be controlled.