The sensing distance for a given application may be adjusted for optimum closing and opening to best suit the application. Here the sensitivity of closure is measured in milliTesla or ampere turns. This is called the pull-in point.  Removing the magnet, the contacts will open at some point. This is called the drop-out point. Hysteresis is another useful parameter and can be adjusted to optimize a given application. Hysteresis is simply the ratio of the closure distance divided by the opening distance. The hysteresis can be critical for some applications.