National Instruments NI 6115/6120 - Manual (Page 79)

Chapter 5 Calibration
© National Instruments Corporation 5-3 NI 6115/6120 User Manual
To externally calibrate your device, be sure to use a very accurate external
reference. The reference should be several times more accurate than the
device itself.
For a detailed calibration procedure for the NI 6115/6120, click Manual
Calibration Procedures at
ni.com/calibration .