The megger is used as a quality control measure to test the insulation resistance to detect any fault in the heater cable jacket. Such leaks cannot be spotted with a regular ohmmeter and help spot any damage to the cable and cable jacket.
Periodically the programming and date/time are stamped to a section of internal memory. This is then overwritten when the next stamp takes place. When the power is resumed following a power outage, the device will revert to the most recent stamp taken.