The Keithley Model 610A Electrometer is an ultra-high impedance voltmeter with full-scale ranges of 0.01, 0.03, 0.10, 0.30, 1.0, 3.0, 10, 30, and 100 volts. Accuracy is within 2% of full scale on all ranges, The maximum input resistance is greater than 10¹⁴ ohms; in addition, the input resistance may be varied in decade steps from one ohm to 10¹¹ ohms by means of the shunt resistors built into the instrument, Thus, the 610A is not only appropriate for measurement in high-impedance circuits, but also can be used where a high input impedance would merely introduce unwanted pickup, The 610A may be used as a direct-reading ammeter from 3 amperes to 10-¹³ ampere full scale, This 14-decade range is covered in overlapping 3x and 10x scales. Accuracy is within 3% of full scale from 3 amperes to 10-¹⁰ ampere, and 4% of full scale from 3 x 10-⁹ to 10-¹³ ampere. Two current measuring methods are available to the user of the 610A, They are selected by a slide switch at the back of the instrument. Normally, current is determined by measuring the voltage drop across a resistor shunted from input to ground, Alternately, on the 10-⁴ to 10-¹³ ampere ranges, negative feedback can be applied to the input of the voltmeter through the current measuring resistor, This largely eliminates the input drop and increases measuring speed, particularly on the more sensitive ranges, The 610A measures 0,2 ohm to 10¹¹ ohms with a two-terminal input, With a guarded input, its range is extended to 10¹⁴ ohms, A 1000-volt external supply would further extend the range to 10¹⁶ 0hms , Unlike conventional ohmmeters, information is presented on the same linear scales used for current and voltage readings. Accuracy is within 3% of full scale up to 3 x 10⁸ ohms, within 5% beyond. As a dc preamplifier, the 610A has a maximum gain of 1000, obtainable in 9 steps of 0.1, 0.3, 1, 3, 10, 30, 100, 300, and 1000. Gain accuracy is within 1% on all gain steps, The continuing stability of the gain is assured by a feedback factor in excess of 100 on any range. The output is either 10 volts for driving high impedance devices such as oscilloscopes or pen recorder amplifiers, or 1 ma for driving low impedance recorders or similar devices, A calibration potentiometer is provided with the 1 ma position for calibrating recorders, A slide switch next to the output connector permits selecting the desired output.