I have a Colnago Super from the late 70s with an unknown seat tube diameter. I wanted to swap seat posts, so I grabbed a 27.2 and got it in there but it was more difficult than I expected. I compared the old seat post and the new seat post by eye and touch before I made the swap and they looked the same, and I'm pretty sure I can see a 2mm difference. Would it be extremely difficult to get a 27.2 into a 27 seat tube? I know it can happen, but I hate to think I might be "one of those guys". I felt the seat tube afterwards for deformation and it didn't seem to be deformed.
Any tips on how I can verify I'm A OK? I guess I might be able to measure the circumference and then do the math to get the diameter, but I don't have a caliper. Could I take the seatpost out and just measure it with a tape measure accurately enough? I don't really wanna change it though cause it's kind of a pain and I got it dialed in at exactly the height I want.