useful commands:
- distance/measuregeom
- zoom ext
- line
- trim / extend
- offset
- "signature": sketch
- donut
- xline: for coordinate axis (infinite lines)

- f8: perpendicular
- f2: console

questions:
+ how to measure exact angle from XY axis? E.g. K1.
  measure
- are donuts really meant to be that small?
+ "ID" command still uses 4 decimal points.
  units
- TODO: validate all corners.
- TODO: measure distances to borders.