Let's see if I can explain this correctly, ha. Hysteresis is the ranges of increases and decreases of a reading of energy (?)
 
Temperatures raise and fall in a fluid motion, so hysteresis setting is the amount of narrowness or wideness of temperature readings.
 
For example, you want your room to be at a constant room temp.  So you set your thermostat's low and high point.  This is like hysteresis.
 
Let's say the range is 5 degrees around room temp. So you have a 5 degree elbow room around where you want the room temp to be.

Can anyone confirm this works?