Since the introduction of the monolithic IC amplifier， there has been a continued improvement in DC accuracy. Bias currents have been decreased by five orders of magnitude over the past five years. Low offset voltage drift is also necessary in high-accuracy circuits. This is evidenced by the popularity of low-drift amplifier types as well as requests for selected low-drift op amps. However， little has been written about the problems associated with handling microvolt signals with a minimum of errors. A very low drift amplifier poses some uncommon application and testing problems. Many sources of error can cause the apparent circuit drift to be much higher than would be predicted. In many cases， the low drift of the op amp is completely swamped by external effects while the amplifier is blamed for the high drift. Thermocouple effects caused by temperature gradient across dissimilar metals are perhaps the worst offenders. Whenever dissimilar metals are joined， a thermocouple results. The voltage generated by the thermocouple is proportional to the temperature difference between the junction and the measurement end of the metal. This voltage can range between essentially zero and hundreds of microvolts per degree， depending on the metals used. In any system using integrated circuits， a minimum of three metals are found： copper， solder， and kovar （lead material of the IC）