A system and a method for monitoring the performance of a subsystem of a forest machine. The method comprises the steps of: collecting data relating to the function of said subsystem or the performing of said function； determining one or more characteristic values to describe the performance continually according to data； and monitoring the variation of said one or more characteristic values in time, wherein, for example, the variation of said one or more characteristic values in time is displayed in the form of a graphic presentation to the user.
