We used to wrap bubble wrap around the top 2 1/2 feet of a 12 foot pole until we got it about four inches thick then completely wrap that with duct tape. Pick a point in the pilots view (10 or 2 O'clock) and bring a blade to that point and set the pole vertically on the ground with the wrapped duct tape just touching the blade tip. Then we marked the spot on the ground, put a red and green grease pencil (can you even buy those these days?) mark on the respective blade and laid the pole down while they started and warmed up. Once they had it up to full RPM we would raise the pole ever so slowly until we got a touch with the blade tip then lower it back to see if we got good marks. Sometimes we could rotate the pole 90* and get a second touch. Then shut it down and make a correction and do it all again. There were lots of conditions to play with such as doing a low RPM check then a high RPM check with tabs zeroed to see if you wanted to tweak a tab or make a PC link adjustment.
The Strobex was a Godsend when it showed up.