Off topic /
It's practical geometry, not maths, and let's not forget the power of proportion either. The vault I'm building doesn't require any maths or measurements, just a compass, a straightedge and a bit of geometrical savvy.........And.......geometry is art, not maths, before you number based freaks start to try and claim it.
Here's a picture of it so far and I might get my hands on it very soon for a winter of fun in the shed.
View attachment 148035
Those joints in the middle need a bit of a tweak, I wouldn't want to get accused of doing too much rough work.
/ off topic.