David Zorn: When measuring droop, you're measuring under the very outside of arm. Pressing down lightly on arm or just under its own weight? Just trying to be sure since seen few different ways depending in who's setup.

Max Machler: Hey David, i put my Car on a flat board and use my Ride Height Gauge to measure droop. Important here, the chassis need to be flat.
I attached Photo for you to show where and how i measure. In this car i used 4.6mm (not the car from the Setup in the Photo)

Source:

M. Machler