Abstract: In an apparatus for notifying machine operators of the necessity for preventive maintenance, predetermined difficulty factors corresponding to the severity of particular machine operating conditions are stored in the memory of a controller. Maximum acceptable values are also stored in the controller's memory. Sensors, detect any one of a number of different machine operating parameters and the duration for which the machine functions under a particular operating condition. These parameters are quantified with respect to one of the difficulty factors most closely related to the operating condition. The quantified parameters are accumulated and compared with the appropriate maximum value. When the accumulated quantified parameters reach the maximum value, an operator is alerted to the fact that maintenance is needed.