Yeah, don't confuse measuring droop, with measuring your downstops. They are related, but not the same thing.
I personally never measure my downstops, as it doesn't appear to be relevant to anything the car is going to be doing, once loaded and sitting on the table. You still have to set ride height, and your actual droop afterwards anyway. I measure RH with a RH gauge, and droop with a metric ruler. I fine tune my left and right sides by looking at the car at eye level, and slowly picking the car up and seeing which tire leaves the ground first. .. .make them the same, then measure the total amount of up-travel before the tires leave the ground (which is your droop).... then increase or decrease equally on both sides as you desire. Piece of cake.
Don't forget, check/reset BOTH your ride height and droop, after changing tires too, as different sets can be different sizes.