If the sensor is replaced, the unit must be calibrated. First measure the actual tank temperature with an accurate thermometer accurate to at least ±1 degree. It should be noted that inexpensive digital and small floating thermometers are only accurate to at best 2 degrees and that liquid crystal stick- on thermometers are only good to ±5 degrees. Accurate calibration thermometers are available from your Medusa dealer.

To calibrate:

1. Press the PROG button to enter the programming mode

2. Adjust the set point temperature to be the same as the actual tank temperature.

3. Press the PROG button two times. The display should now read "CU".

4. Press the ALARM/SET button and, while holding it down, press the PROG button. Release both buttons. The display should show the measured aquarium temperature. Now the unit is calibrated but the set temperature needs to be reset to the desired tank maintenance temperature.