I once worked on an engine that had a time/temperature recorder. It was like an odometer that worked like a variable-speed clock. When the engine ran at a stable EGT, the "clock" accumulated counts at a fixed rate. Increase the EGT 20C, and the clock runs twice as fast; decrease 20C, and it runs at half speed.
So, the counts accumulated are representative of the turbine life consumed.
BTW, the pilots hated the gizmo, because it was a telltale of engine abuse.
