If the unit is not calibrated properly, the OSM neXCalibrator has two resistor VR2 variable resistor 2 for voltage calibration and VR1 variable resistor 1 for current calibration. You should be able to access these resistors by removing the back cover. It is possible to calibrate the unit yourself, by connecting the output to a precision multi-meter or you can have it calibrated by a professional. Once the calibrator is connected to a multi-meter, ramp up and inspect the accuracy of the each step. Ramp up to the last step; use either VR2 if calibrating for voltage or VR1 if calibrating for current output, to adjust the output. The display has one LSD so it is not the ideal metric for determining the accuracy of the calibrator.
To see more information about OSM neXCalibrator follow the link: neXCalibrator