Good addition to my list. Also, the mechanical connection between the bimetal motion and needle motion inside the gage is likely very nonlinear. In modern cars, those signals go thru a digital processor. If there is a dash needle, it is just a motorized positioner, controlled by the processor. The designers could linearize it all in software, though not sure they do since I think they still purposely do the "fake good mileage at top end of needle" trick.
