We're up to Post #100 and still no one has mentioned how absolutely essential a chinagraph pencil was when performing tracking of helicopter main rotor blades after maintenance. Each blade tip was liberally marked with a different colour chinagraph, then with the rotors turning at normal RPM, a "tracking flag" was slowly - very slowly - moved to gently "kiss" each blade tip in turn. This left a coloured mark on the flag corresponding to the vertical position of each blade relative to the others. From this adjustments could be made to get the blades "in-track" which helped, but didn't guarantee, that the helicopter would be smooth in flight.