Why not to make astigmatism tool as default cm measurement tool?
Some may have (more or an) astigmatism, even don’t presuming that.
Also, you may add a circle in center of those two lines on the rotable part.
It will be easier to assess axis degree, when focusing on circle (some part of circle becomes clear, so your axis is 90 degrees opposite to that degree).
Also, why not to add some red, blue or such color lines to acquire more balanced (not too high, not too low) results based on summary of those lines.
Personally drawn a similar tool because I don’t have a printer.