Abstract: Apparatus and method for measurement of the activity of a central processing unit of a data processing system resulting from the execution of a program or series of programs. A value is initially entered in an arithmetic circuit. Each time an instruction is executed, a quantity related to the amount of activity required to execute the instruction is decremented from the arithmetic circuit. When value in the arithmetic circuit reaches zero, the operating system is notified and a decision whether to continue the program or initiate some other activity in the data processing unit is made. The usage of the machine is therefore determined by the number of times the arithmetic circuit has reached zero during the execution of a program and by the quantity remaining in the arithmetic circuit when execution of the program is complete. Provision is made for other measurement modes such as decrementing the quantity in the arithmetic circuit by a clock.