A manometer can be used to find TDC.
A manometer is simply a U shaped tube with a water or oil "indicator" in it. Air pressure or suction at one end of the U causes the indicator to move.
For our Z application, a drilled out spark plug, 3' length of plastic tube, and a few ml of coloured water is all that is needed.
Note that a one thousandth inch change in the piston is nearly 1/2 and inch of water change.
