"Etwas einpendeln" meant originally to use a pendulum, or rather a weight suspended by a string, to adjust something incrementelly until it is level. So "sich auf etwas einpendeln" describes an action where something does this on its own. Ups and downs in life can move this amount (context for "Maß" is missing, maybe a different translation is better) upwards or downward, but in the long run the personal sense of well-being will even out on the inherited level.