The upper hour display has no reset and operates simultaneously with the lower display.
The lower display is a preset hour meter programmable between .1 and 99,999.9 hours and can be changed at any time. Once the preset value has been determined, only the elapsed time is shown. When the time reaches its preset value, the LED illuminates and the SPDT output is energized and remains in this state until it's reset.
In case of a power failure, the preset value and the accumulated hours shown on the displays remain unchanged but invisible. Once power returns, the displays indicate the hours shown before the power failure. Also, both the output and the LED are in the state they were before the loss of the power.