The Keithley Model 510 Megohmmeter utilizes a unique logarithmic circuit to present six decades of resistance on a six-inch mirror-scale panel meter. With so great a dynamic range, range switching is not necessary, and the speed and ease of measurement are greatly increased. Because of the logarithmic ocale, the usual high-end scale compression of a conventional ohmmeter is eliminated. An accuracy within l$ of the scale length is maintained at every point on the scale; this is equivalent to an accuracy of about lO% of the resistance being measured. It is limited only by the meter accuracy, and is about as good as conventional megohmmeter circuits at mid-scale, but superior to conventional circuits at other than mid-scale meter readings. Test potentials of 5, 50 and 500 volts are furnished. They are useful in measuring voltage coefficients, and offer freedom in selecting a safe potential for all test samples. I -1 5’0