The MXP series of pressure regulators put out a ratiometric output, not an absolute voltage/kPa. Again, look at the formula in the datasheet:
Yes, that makes perfect sense now after your explanation dilbert and
I've had time to think about it. That is also why I get a value of 1023
at the max pressure even if I only have 4.95 volts at the sensor. I
think I will use the DEFAULT for now.
If I needed more accuracy and had a spare analog input I guess I
could measure the Vs but it seems in my case the error is only 1%
max (4.95/5) so it might not be worth it. And if the sensor
output is a percentage of Vs anyway the error is even smaller.
Assuming a good voltage source, is the Arduino 5v regulator usually
fairly accurate?