state.CFG - two accumulated_time figures?

[Sender46]

My state.cfg file for the Arrow III (located in C:\Users\Graham\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\SimObjects\Airplanes\JF_PA28_Arrow\state.CFG) reads:

[engine.0]
accumulated_time=16.784174
accumulated_time_hobbs=19.689758

The first figure (NOT the second one) matches the Hobbs meter reading of 16.7 in the aircraft, which appears to be about the time spent in it since being reset by the last update.

Before that I must have spent 100 hours or more in this aircraft.

So where does the 19.689758 figure come from?