Hephaestus RC How-To Droop Measurement:
Step 1 - start by measuring the wheel we will use (can use two) fig.1
Step 2 - place the wheel in a hard and level surface.
Step 3 - take wheels of the car, place it on top of the wheel(s) previously you put on the hard and level surface.
Step 4 - for each axle, measure with a caliper the distance between the surface and the top of the axle fig.2-3,subtract the wheel measurement.
Step 5 -??????????

For consistency in your measurements one should always use the same wheel even across different platforms like truggy or 1/10th 2wd buggy provided the arms don't touch the hard and level surface.