I was able to perform some accuracy testing with a Rigol DM3068 6 1/2 digit desktop digital multimeter. This testing provides another level of validation of the accuracy of this project. I tested two units. The first unit was in the constant reference voltage mode. The second unit was in the adjustable reference voltage mode, with various current commands set. The below tables shows the actual commands (which are sometimes slightly odd numbers due to the limited bits of the DAC in the adjustable reference voltage mode.) The accuracy claims are from the DM3068 datasheet for the 1 Year accuracy specification. The accuracy is given in % of reading and % of range, so both are shown here. The first table consists of measurements for the constant reference voltage mode.

Note that for every single measurement, the measured error was smaller than the claimed 1-year accuracy of the DMM used, indicating that this device is precise to a higher level than I can measure!

The table below shows the measurements for the adjustable reference voltage mode.

Again, for every single measurement, the measured error was significantly smaller than the claimed 1-year accuracy of the DMM used, indicating that this device is precise to a higher level than I can measure!