Purpose Of Hole In Edge Of Flywheel, What is it for? Options

[Osnabruck914]

914-4 2.0 Liter Engine

In the engine compartment looking backwards towards the rear of the car, there is a view port at about the eleven o'clock position of the bell housing through which you can see about an inch or so of the outer extremity of the flywheel. There is a perfectly machined dime-sized hole in that area of the flywheel that passes by that port as you spin the flywheel. When at TDC for Cylinder #1 that hole just starts to appear at the edge of the view port. It is not centered to it. What is it for? Is it another TDC reference, which I doubt, as it is a relatively large hole and does not center to that view port. Is it where material was removed to balance the flywheel?

When I adjust my valves I use the factory scribe mark on the circumference edge of the flywheel, plus another mark I painted 180 degrees opposite, plus a 0 degree mark I have on the fan to determine TDC points. So I am puzzled by this hole in the flywheel.

Probably a stupid question, but I sure want know.

Osnabruck914