I too have seen some inconsistent methods. If you move you lower arms up or down, then the droop seting will change with the same reading on a droop gauge!...
Here's my way of getting consistent compareable results. You will need...
*tools for adjusting droop
*round object to balance chassis on (a small hex driver is great) approx 12mm diameter works well.
*tweak gauge (I use a laser type)
1) Put on the wheels that you are going to use. You will also need shocks on your car too... spring rate is irrelivant.... just have some on.
2) Wind preload down alot! (compress spring) This pushes the wheels down as far as your droop setting allows.
3) Using a ride height gauge, adjust your droop screws until you get the max downtravel setting you desire. Measure from the front or rear to get that ends setting. Try to keep droop screws even (this will be corrected later).
4) Once max down travel is set (droop), get a round object such as a screw driver (approx 12mm in diameter is great) and place it under the front bumber IN THE CENTER of the car. This will lift the front wheels off the ground and allow the chassis to rotate around the centerline.
5) Using a comon reference point (like motor armature) measure the chassis height on both sides. Adjust rear droop screws a little at a time in opposite directions until you get the same reading on both sides.
6) RECHECK your rear droop by taking round object away and checking ground clearance. If it is too low/high, adjust accordingly and repeat steps 4 and 5.
7) Place car on tweak gauge (as per normal instructions). You should see any difference between front/rear settings on your gauge. Using front droop screws, adjust in opposite directions until it reads level.
8) Once again recheck with chassis on surface only to ensure droop setting is right.
9) Adjust rideheight to what you need and your ready to rock!
This method will give you balanced droop and will allow for any chassis tweak. Best of all, it will give you the same settings no matter what rollcenter settings you use or tyre diameter.
If you don't have a tweak gauge, you can simulate it by lifting the front end off the ground with a fine tool (like a kinfe) in the center of the chassis. Adjust by looking at which wheel leaves the ground 1st. This method is a little more crude as it dosen't allow for play in the shocks.