National Instruments AT-MIO-16X - Manual (Page 223)

Chapter 6 Calibration Procedures
© National Instruments Corporation 6-11 AT-MIO-16X User Manual
output to 5 V and adjusts CALDAC4 and CALDAC5 until it measures
5 V between each analog output and AO GND. The gain error is always
calibrated immediately after the offset is calibrated. Notice that
CALDAC4 and CALDAC5 adjust the gain by varying the values of the
internal DAC references. Hence, the gain of an analog output channel
cannot be adjusted under software control if the channel is using an
external reference (but the offset can still be adjusted).