Start with the work in front of you.
Bend Notes is the working title for a tool I built with a plumber around a specific part of the job: translating a tubing layout into measurements and bend marks. I wanted the software to follow that practical sequence, with a clear relationship between the measurements going in and the marks coming out.
That made understanding the workflow as important as writing the calculation. A useful answer needs to make sense at the point where someone measures, marks and bends the tube.
Keep the reference in view.
The prototype uses manufacturer tables and explicit measurement references. Those choices make the source of the calculation inspectable: the result has a basis that can be checked against the tool and material being used.
I built this as a web prototype so the interaction and the calculation could be developed together. I plan native iOS and Android versions alongside the web app, carrying the same focused workflow into those formats.
Know what a test establishes.
Worked-example tests check the calculation against recorded examples. They give me a way to catch changes in the arithmetic and measurement conventions as I develop the interface.
A matching example does not establish a fabrication tolerance. Physical results still depend on the material, bender and execution. I keep that distinction visible when describing the prototype and deciding what needs validation next.