With the TDC mark lined up with the pointer both cylinder one and cylinder six will be at top dead center. One of them will have both valves closed and the other won't. This is obvious by looking at the rocker arms. And the mark lined with the pointer is as accurate as you need to be.
You don't need a bolt in the spark plug hole to determine this. You don't need a manometer hooked up. This is complicating a simple procedure and probably confusing people in the process.
