Go to the gear symbol in the app. Select cm instead of inches. Your entries will be shown in mm and you can just type the number without conversion. You can also add in or mm to the end of the number to avoid conversions.

I wonder if this is a well known math library? I bet they didn’t build their own equation parser, they probably used a framework that included it or had an add on module. Anyone familiar with anything like that?

Indeed I do: https://github.com/josdejong/mathjs is the library I used to implement that - when I set it up to take inputs like “.2 in - .008 mm”, all the math constants came along for the ride, which made for some amusing moments when testing what I thought were non-numerical inputs. I was going to remove the math constants, but they’re pretty fun!