Keithley 2601B Reference Manual page 751

Series 2600B System SourceMeter® Instrument Reference Manual Appendix B: Calibration
3. Capture the reported voltage measurement.
4. Calculate the current from measured voltage and characterized resistance.
5. Verify output current accuracy for each of the currents for the 1 nA to 100 nA ranges listed in the
table titled "Model 2634B/2635B/2636B output current accuracy limits."
2600BS-901-01 Rev. B / May 2013 B-9