DAC linearity

[timblackwell]

I am struggling to use your code to achieve the desired results and I believe the issue is the output from my DAC is also non linear. I have taken these measurements with an external voltmeter on the pins for various DAC output values:
200 -> 2.52v
100 -> 1.31v
50 -> 0.71v

When running the test, the program declares Should be: 1.26 measured: 1.26 by setting the output pin to 100 and halving the known voltage at 200, but when if I measure externally the reading is 1.31v.

I wonder if this program maps the characteristics of the DAC to the ADC but as the DAC is non linear, we still do not have accurate readings from the ADC?