Using a simple mathematical formula, it is possible to calibrate analog sensor readings. If you are using a COTS analog sensor, and have access to a high quality, or more reliable sensor, taking several readings can provide a coefficient and offset for calibration.
In this example, a voltage sensor is implemented with a voltage divider. A digital multimeter is used to glean more accurate readings, and a coefficient/offset is generated with Octave/MATLAB.
All source code can be found on GitHub.