Press both the SELECT and SET buttons simultaneously for 3 seconds and release. You will see F for Fahrenheit or C for Celcius. Press and release the SET button and you will see 12 CLOC. Press the SET button and you will see the differential. Use the arrows to adjust the differential from 1-3 in .5 degree increments. When you are finished you can either press the SET button until you return to the main screen or leave the thermostat and it will return to the main screen in about 20 seconds.