Ryan B. said:
In theory it should be, but if you are building a high performance engine, or have stroked it, etc. It could be a degree or two off.
My big block is just a hair maybe a degree off from the stock mark on the balancer in relation to where my aftermarket pointer is.
Marking say .050" down in the hole on either side of TDC and splitting the difference will get you EXACT.
These are just a few tips i've learned building a race engine.
Adjustable, as in you can adjust the depth the piston stop screws into the spark plug hole?
You know it is at Exactly TDC by the method i described in an earlier post...
Spin over the engine very carefully until it stops on the piston stop. scribe a mark on the balancer. Now spin the engine over the other way until it stops. scribe a mark.
Exactly half way between those marks is EXACT TDC.