I often work with archways and if I draw them on Styrodur I use coins, bottle caps or whatever lays within reach. To make live more relaxing I decided to make a template. Now I can quickly draw windows, doors and archways. Next I designed a second template that helps me divide the archway into 5, 7 or 11 equal parts in a way that the stones looks good in size and are drawn using the right angle.
The picture above is a small test piece that show the effect of working with this template: