If you are comparing your Freeze Alarm to a wall thermostat be sure to move the Freeze Alarm very close to the thermostat to be sure they are sampling the temperature at the same height and area..example-temperature can vary several degrees between the floor and 5’ . Also be sure the thermostat or thermometer you are using is also accurate. If you still find the Freeze Alarm is inaccurate it may be defective or unsuitable for your application. The Freeze Alarm models FA700, HS700, FAI and FAD2 do not allow calibrating. If accuracy is important please consider the Sensaphone 400 and Sensaphone 800 which allow you to calibrate to 1 degree accuracy.