Secondary Offset question.

I got my Feathertouch focuser in today and mounted it. I had to square it to the secondary. To do this I had to work out the offset for the optical center vs. physical center of the mirror.
My question is this.
I used a formula that I found on the internet as follows.

Diagonal offset = Diag mirror size divided by F/R X 4 then X 1.414

Diagonal Diameter = 2.6” = 66mm
F/R = 4.9 X 4 = 19.6
66mm divided by 19.6 = 3.3673469mm
3.3673469 X 1.414 = 4.7614285mm
4.7614285mm = .1874574” = 12/64” (6/32")
Offset is measured from true center of diagonal mirror ellipse away from the primary mirror.

1 millimeter = 0.0393700787 inch

Well after I finished I found 2 more fomulas! Great! They both came out to about 9/64" instead of 12/64" offset.
Well, it was a bitch to square the focuser because you had to remove the focus knob assembly and adjust the leveling screws and tighten the bolts then assemble it and check it with the laser.
So no I am wondering, is the fomula I used correct? If not ,will it make any real difference if I am off 3/64 or 4/64" on the optical center?
I am willing to readjust it if needed, but I am not looking forward to doing it again.
:^(
Floyd