“…For simplicity, only angles of α degrees that are divisors of 360 degrees are considered, so 360modα equals zero. The 24 divisors of 360 are 1,2,3,4,5,6,8,9,10,12,15,18,20,24,30,36,40,45,60,72,90,120, 180 and 360. Note that, however, the methods themselves are in no way restricted to those rotation angles.…”