As I said each to their own
I'm not sure why you're making it so complicated.
Even easier using QCAD where you can just type out the "equation" as fractions of an inch when you enter a dimension so to use your example this will work in QCAD type 1' 2 1/2" * 7/12
Again it's simply what you are use to, I see that and think it's 1/64 less than 24/64, 24 is divisible by 8 so if you had to mark out 23/64" it is quite simply 1/64 less than 3/8" and my ruler has a graduation line for that, whereas the metric rule doesn't have a graduation mark for 9.128 mm. It's just very useful to be able to switch from one to the other as the situation dictates.