Additional Information
Calibration is important because the performance of any given analog-to-digital converter can vary according to temperature, input voltage, time, and other factors. Because of this, calibrating a DMM or data acquisition device must take these two factors into consideration.
When a DMM or DAQ card is calibrated, specific calibration constants are stored on the board’s EEPROM memory, a read-only memory whose contents can be erased and reprogrammed using a pulsed voltage. These constants are used by the driver software, (DAQmx, NI-DMM, etc.) to return the appropriate value for a given measured voltage. This technique is absolutely essential, because no analog-to-digital converter (ADC) is capable of producing a perfectly linear response. In addition, the calibration constants can be adjusted through external calibration.
To learn more about performing external calibration using LabVIEW, read Can I Perform an External Calibration for my DAQ Device in LabVIEW?.