I was trying to draw up some paper models my children could fold and glue together and needed to work out the length of an arc so it would bend into the correct shape.
I am old enough to have been taught technical drawing with paper and pencils so I probably could have worked it out had I stuck with it, but having been spoilt with the use of CAD at work (or just my lazy streak kicking in) I thought there are easier ways to do it and waited until my lunch break at work to draw the more complicated parts.
Just to add if Serif wanted to go down the separate compatible app route "Affinity CAD" would have my money.