I have never seen that device before - we only ever used the round protractors here in Australia. But yes, if you can measure the angle directly, then go for it. However, if you wanted to be very precise with the angle for some reason (and some people are like this, including me ), this is possible with my ruler method.At least in Germany every pupil sitting the first time in a math class is obliged to own this tool called 'geometry triangle':
For example, the 1:10 ratio gives you an angle of 5.7° (atan(1/10), but if you wanted it to be exactly 6° for some reason, you can do the ratio at 1:9.51 rather than 1:10, which in my scenario would be 200mm horizontally and then 21mm vertically. The longer the distance the more precise you can get.
But good job on the tool, I need to spend some more time going through it in detail. I got sidetracked by solving my blunt chain issues with other solutions - turns out it probably wasn't the chain at all.