Collimating without primary

I find it much easier to center and allign the secondary with the primary out of the picture. I usually only have to do this once in a blue moon, but after taking a scope appart for some reason or another it is much easier for me to adjust the primary when I know for sure that the secondary is centered in the focus tube and shows (centered) where the center of the primary is. (Or will be when I uncover it.) I have a big X on the mirror covers of a couple of open-tube scopes for this. When working on a Meade 8" dob, I usually just take out the mirror and put a thin piece of paper (again with an X) over the end of the tube.

Am I the only one who does this?

Charlie