[cr45]

As the last decimal place is dancing around you could try measuring in cm of H20. The readout will only go to 1 decimal place - a resolution of 1mm of H2O. This resolution is approx 4 times courser than 0.01" resolution in inch H20 mode but should provide a more stable reading.

Just 1 problem though, this represents a resolution of 10 Pa which is not going to be accurate enough for a lot of locations on a car particularly at the rear.

It looks like damping or the average function will have to be investigated.