The "economy" gauge that MB put in some of their models display just how one maintains throttle...it measures manifold vacuum pressure.

Data like that is fairly easy to collect for a computer. The FSS system (my ML has it) supposedly figures out my next service interval based on one of these driving parameters...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car