cold when they are closer. hot they expand. to adjust temperature, look the thermoterer of the inside temperature. turn the thermostat off when termometer show the wanted temp..y if it turn off before the wanted temp., turn it on til it riches wanted temp.
Heat makes the wafer expand, that, at some point pushes on the button on the snap switch shutting off the heat. As the wafer cools it contracts lifting off the snap switch, turning on the heater.
The idea is to get it to shut off as close to 99.5 as possible & to come back on at 99.5. Most wafers aren't that accurate, so you probably end up with it shutting off at 100 & coming back on at 99. If you get one that is that accurate, you've got a good one, but remember its ADVERAGE temperature you want. So if it comes on at 99 & off at 100 the average is 99.5 - perfect.
One last note - once you get it set, make sure you lock the set screw, normally with a wing nut, to keep the adjustment from moving. You may need to lock it down & loosen it, & reset several times to get the perfect temperature, because when you lock it, it can change the distance between the wafer & snap switch, changing the temperature.. Kinda of a pain, but once its set, it's set
you typically want a thermostat to turn off a degree or two above the desired temperature and two or three degrees below. This is because of a symptom called historicises (not sure of spelling). This is when thermostat is set to an exact temperature for the on and off. What happens is the thermostat clicks back-and-forth in the matter of less than a degree change. Therefore the thermostat either never turns off or never turns on completely and what you get are burned out any circuits acting like an arc.