The thermostats I used on my undertank heaters was a love brand from homershams and the hysteresis coud be sdjusted. I use a digital thermometer that is accurate to 0.1 grees which also cae from there. It is portable so I use it to check any tanks, reptile enclosures or insect breeding setups. The thermostats were $340 each and three got munted in the Feb quake. Got insurance but have not replaced yet.