Abstract: A locking apparatus is coupled to and incorporated within an electronic instrument to ensure that the instrument operates within a predetermined set of performance parameters. The instrument's operating characteristics will be tested and measured by an external, automatic test system as is typical in the manufacture of many electronic instruments. The locking device will prevent the ordinary operation of the instrument until the instrument has successfully passed the tests administered by the automatic test system. Upon successful completion of the tests, the test system will communicate a signal to the locking device. Upon receipt of the control signal, the locking device will "unlock" the instrument allowing normal operation. In order to ensure that routine calibration takes place, the locking device can be instructed to periodically disable normal operation of the instrument until another performance test is administered by an automatic test system.