That's a bit brain bending.... dang! Is this because pressure itself is logarithmic?
No, it's just how accuracies are expressed regardless of the sensor they apply to
The datasheet of the $100 sensor says the max error is .2% FS (full scale) where FS is 3500 Pa and 1.5% of the measured value (reading).
So, you're right I was taking .2% of the full scale and applying it at the bottom.
So, the accuracy error accumulates as the voltage goes up..., that is at 0 mV when there's no wind so 0% error?
At the max reading that's the max error (.2% of 3500 Pa)?
Saying 0.2 % FS for a 3500 Pa sensor is the same as saying 7 Pa. So the total error can be expressed as 1.5 % + 7 Pa. For example if you measure 200 Pa then you can have a max error of 10 Pa (1.5 % * 200 + 7).
At 0 Pa real the 1.5 % error disappear but you still have the 7 Pa error.
Usually the base offset can be calibrated and never changes much so you only deal with linearity error.
BTW 3500 Pa is a bit much so I'd recommend a 1500 or 2000 Pa one, and you can find sensors with a better accuracy, both of which will give you better results.
I'm concerned that it would cost more to buy a signal generator and an o-scope than it would be replacement parts.
No need of a sig gen, just toggle a arduino pin at 40 kHz But the scope is almost mandatory if you do stuff like this, else it's like driving while being blinded... You can find used 2x 20 MHz scopes for next to nothing on ebay/craig list/... (or even free if you know someone who handle that stuff in universities and co for example) which would cover 99 % of your basic needs (and 100 % for this project). EEVBlog has a good video about finding them