Instrumentation V: Toward serviceability: Built-in calibrating and self-testing features are two ways of easing servicing problems. But digital circuits present unique problems

When a $1000 voltmeter goes out for repair or calibration thereby paralyzing a $100 000 automatic test system, the system designer's nightmare of small instruments controlling large, expensive systems has become a reality. Of course, the need to service parts is an inevitability as is some degree of unreliability. But as the demand for more complex and powerful instruments increases, so does the challenge to increase their reliability while at the same time decreasing the frequency with which they must be serviced.