The usefulness of difference amplifiers is limited by the fact that the input resistance is equal to the source resistance. The pico-ampere offset current and low current noise of the LT1077 allows the use of 1m source resistors without degradation in performance. In addition, with megaohm resistors micropower operation can be maintained. This is a classic difference amplifier configuration, but with unusually hi-value resistors. The particular input characteristics of this opamp provide the ability to retain accuracy with such high resistances without introducing undue error from noise or dc offset.