Abstract: A machine operation monitor is provided for detecting malfunctions during execution of a machine cycle of operation irrespective of the activity being performed. Load levels of machine member driving means are periodically sampled and compared against limits computed by the monitor. The limit calculation uses net force or torque measured by storing load level samples during two preparatory executions of the machine cycle of operation. During the first execution a finished workpiece is produced using good tools. During the second execution no workpiece is present. The differences between load level samples taken during these two executions represent the net force required to perform work on the workpiece. The monitor responds to synchronization signals to maintain correspondence between load level samples taken in successive executions of the machine cycle. The monitor also responds to monitor off signals to suspend monitor operation during periods of no activity in the machine cycle.