Hey fellas....for a long time that was the only way....a bit of grease pencil and a tracking flag...or a bit of masking tape stretched between a couple of sticks.
For tail rotors it was a stick with a grease pencil taped to it....and slowly poked into the tail rotor.
There was a technique to swinging the tracking flag into the blades....and not getting the pole smacked out of your hands the wrong way. The wrong way could get you knackered in a split second!