Due to many questions about Droop Gauge measurement, we realized a Droop Gauge Comparison Chart.
http://blog.hrcdistribution.com/setups/E4RS_II_EVO_Droop_Gauge_Comparison.pdf
Measurement under wheel axles: this is realized with SpecR droop gauge, to measure distance between setup board and wheel axle, when the car is on 10mm blocks.
Measurement under arms: this is realized with Team Magic or any similar gauge (like Hudy by example), to measure the distance between the setup board and the suspension arm (not the C-hub or the upright).