[dcb]

Last thoughts (sorry if this turned into a hijack)

Weight between tests has to be consistent (within 1% would be nice, 30lbs for a 3000lb car, more than 3 gallons of gas). This part will take a bit of ritual, i.e. jump on the scale clothed, only test after a careful fillup , keep same weight of objects in car (can substitute items, but put on a bathroom scale to determine weight change). Also important to reweigh (i.e. truckstop) occasionally to validate your techniques and throw out or correct any previous tests since the last valid weigh in if your approach is off. Store current weight in configuration

The timing of crr (and cda) would not be on strict mph boundaries because of the low pulse counts from the vss, but rather should be based on average pulse lengths within a precalculated range of pulse lengths and the time between the first and last pulse in the average.

It is correct that temperature and Crr are interrelated, but it is probably safest to just redo the crr portion first in the same session as the cda tests, and again at the end of the cda tests.



So "simple" test procedure is (after weight is determined) without hardware changes or custom web appliances:
*warm up
*update the temperature and barometer settings in the configuration (i.e. from weather.com)
*locate your long flat test spot
*fillup
*activate the cda/crr routine with the menu, follow prompts
*in one direction
*do a crr test i.e. 5-3mph
*do 3 cda tests i.e. 55->50 in a row
*do a crr test i.e. 5-3mph
*turn around
*do a crr test i.e. 5-3mph
*do 3 cda tests i.e. 55->50 in a row
*do a crr test i.e. 5-3mph
*read your cda, which should be about as accurate as your weight and temperature/pressure readings and your ability to drive in a straight line. Within 1%? not entirely sure. probably more likely if you have an accurate barometer/thermometer in the car and are really careful about weight and fillup procedures.

from 0 degrees C to 35 degrees C, the density change swing is a total of about 11%
so any errors in temperature measurement will likely be reduced to 11% of the original error when expressed as a density error. Every degree centigrade is about a %0.35 change in density.

For pressure it is a similiar story, if the typical pressure range is 1010 to 1034, that is a total density swing of 2.5% and a 2% error in absolute barometer readings is a %0.05 error in density.

If I recon correctly. It seems chances are good of getting reasonably cheap, easy, and accurate CDA to me though that doesn't need any extra hardware.