The 261 Picoampere Source is a secondary standard for calibration of picoammeters and electrometers. It is a "passive" source, consisting of a selectable 0 to 10V voltage in series with a specially selected and tested hi-meg resistor. Output of 10E-14ampere to 1.1 x 10E-04 ampere with 3 dial resolution Accuracy varies from ? 0.25% to ? 1.6% depending on range