I'm preparing a new company template that makes our AutoCAD jobs look more similar to our Revit jobs and corrects many of the quirks that have crept in through the years. I'm trying to make it as bulletproof as possible but have discovered an issue that seems to be deeper into the program than I am capable of tickling, and think it's something that Autodesk should address if for no other reason than to restore confidence in the program. I'm not sure what the ramifications of it would be in practice, but I hesitate to promote a new standard that I know has potential flaws in it. I first discovered the issue with AutoCAD 2018 but find it repeatable in AutoCAD 2021, and on different computers. Here's what it takes to replicate the issue:
Make a new drawing using either the acad.dwt template or Open with no Template - Imperial.
So far viewports in Paper space at all scales will have a correct correlation between Annotation scale, Standard scale, and Custom scale.
Now set Units to Architectural and Precision to 1/256".
Most viewport scales correctly correlate between Annotation, Standard, and Custom, but these scales have a mismatch with Custom:
Annotation/Standard __ Custom Scale _____ Custom Scale
Scale: _______________ should be: ________ is:
___1"=1'-0" ____________ 1/12" ___________ 21/256"
_1/2"=1'-0" ____________ 1/24" ___________ 11/256"
_1/4"=1'-0" ____________ 1/48" ____________ 5/256"
_1/8"=1'-0" ____________ 1/96" ____________ 3/256"
1/16"=1'-0" ___________ 1/192" ____________ 1/256"
It appears to be some kind of weird rounding phenomena in the custom scale numerators, but I can't fix it and I just don't know where or how it would come back to bite us in actual use.