I'm not sure how you are doing that with your caliper, fastbroshi. I'll have to go look at some and figure that out. I would have done it like cornandp suggested so I had the center distance and the diameter of the forks to CAD. Maybe I'm not getting what you mean. I'm not a machinist or anything, just an amateur. Hmmmmm.... off to check out calipers since I'm apparently wide awake tonight. Ya never know what you're going to learn around here.
I'll see if I can explain. My favorite crayons don't work over the internet so bear with me. Given our two identical circles, or the holes in the triple for our fork tubes, they'll have the exact same diameter, 35mm on a CB550. They'd have the exact same radii too, or the orange measurement, which is 17.5mm.
We can measure from center to center(the pink line) or, from the same point on each circles outside diameter. This is the blue line. Both measurements would be identical. Which one you use just depends on your measurement tool and the easiest way you can take your measurements. Hope I didn't mess that up.
And I forgot to measure that yesterday morning, sorry. It's like 5 AM when I get off. I'll try and remember to do it if you still need it.