Wow, that's interesting. Brings back memories, too...
When I was in school, we had to learn how to inspect and track rotors using something called a "tracking flag." This was basically a piece of cloth attached to a pole. The tracking was checked by coloring each rotor tip with a different color grease pencil (or chalk), running up the helicopter to whatever setting(s) the manufacturer specified, and moving the flag until it touched the tips.
The procedure for tracking the tail rotor was similarly enjoyable. We taped a grease pencil to a broomstick and sloooowly moved it toward the rotor's plane until it just barely touched, then looked for the grease marks.
We did this in teams of three: one managing the flag (or broomstick), one in the cockpit, and one safety observer with a fire extinguisher and a set of rosary beads. (Okay, j/k about the rosary beads.) We rotated so everyone had a chance at each station.
Amazingly, there were never any serious incidents or injuries that I know of.
-Rich
