Or, more accurately. the heavy side of the "Prop Disk".

If you think of a prop correctly, it does not have two sides, it has 360 degrees.

So think of it as a disk.

If you put a CD into your prop balancer (and it was perfectly balanced), it would stay in which ever position you put it in.

If a certain area always fell to the bottom, that side is heavy.

Same thing with a prop. If you cocked the prop below at a 45 * angle, and it leveled itself out, then side "D" is heavy.

If it always stopped with "E" at the bottom, Blade "A" is not heavy, area "E" is (or "F" is light)

So, to paraphrase Dennis, put the heavy "area" opposite the piston at TDC.