The Model 485 Autoranging Picoammeter provides 100fA sensitivity with 41⁄2-digit resolution in a low-cost, highly sensitive, easy-to-use instrument. The 485 measures DC current on seven ranges covering 10 decades from 100fA to 2mA. The input can withstand overloads as high as 1000V (with 100kΩ limiting resistor) for flexibility in a wide range of applications in test, research, and student labs. An analog output linearly converts the incoming current to voltage for hard copy output or control loop applications. In addition to 100fA sensitivity, the 485 has both excellent accuracy and low voltage burden. One-year accuracy on the most sensitive range is an impressive 0.4%. The 485’s input voltage drop (burden) is actively constrained by feedback techniques to less than 200μV. Thus the 485 makes high accuracy current measurements even in circuits with very low source voltages. The 485 has several features that facilitate measuring low current. In the autorange mode, the 485 maximizes resolution. The REL button makes readings relative to the baseline (the reading prior to touching the button). The LOG button converts the display to the logarithm (base 10) of the absolute value of the measured current. Digital calibration is performed from the front panel or over the bus. A 100-point data store buffer collects and stores measurements at one of six automatic reading rates from three per second to one per hour, or manually with the STORE button. Minimum and maximum readings are continuously updated at three per second in the data store mode. The addition of the Model 4853 IEEE-488 Interface to the 485 provides fully programmable computer control. For isolation from the power line or for portability, the 485 can be battery powered with the Model 1758 Rechargeable Battery Pack