Infinity has, for most troops, a 180° front arc for Line of Fire and almost all actions. Other games have similar arc requirements – Full Thrust uses six 60° arcs on it’s starships, for example. To help me do the 180° arcs on my Infinity bases, I’ve whipped up a simple little measuring widget in Inkscape.
The two PDFs below (one Letter, one A4) are designed to be printed out to help with marking arcs on the bases of figures; there’s four quadrants for 90° or 180° marks and Full Thrust/hex-side 60° lines as well. The rings are to help centre your bases accurately; they start at 20mm and go up by 5mm then 10mm all the way to 60mm; the rings are 20mm, 25mm, 30mm, 35mm, 40mm, 50mm, and finally 60mm.
Use should be fairly obvious – centre your bases on the marker, put small marks with a pencil or fine paintbrush at the arcs you need to specify,