I have been playing around with some joinery details, and it came to me that whoever drew them was thinking as he drew, with lines and so on. Once he had those lines, he saw no reason to alter them. Which is fine.
Only problem is, that he wanted to generate more sections based on them, things got a little messy, to the point where he must have said to himself:
"Funny? That dimension should have been 139mm....it is not actually that, on this model....oh well, let's just do a quickie here and alter the dimension text to read what I want instead of what it actually is".
Where's my big hammer?
The trouble is, when you are designing, it is wonderful to use lines etc, but once you have zeroed in on a particular size, make it into a block, so you don't inadvertently stretch it, plus you can reuse it, confident in knowing that it is a set piece of geometry.
I'm thinking here of a sectional view of a window sash.