So is the measured response graph linear only because of the spacing between the readings?
It was critical that it never "step backwards", each step had to be equal or greater than the previous.
MonotonicA sequence increases monotonically if for every n, Pn + 1 is greater than or equal to Pn. Similarly, a sequence decreases monotonically if for every n, Pn + 1 is less than or equal to Pn. A DAC is monotonic if the analog output always increases as the DAC-code input increases. An ADC is monotonic if the digital output code always increases as the ADC analog input increases. A converter is guaranteed monotonic if the DNL error is no greater than ±1LSB
My end product also included at least 8 trim pots and was generally regarded with horror by those more knowledgable.