isometric angles

when tackling angle work there seems to be merit in restricting the angles to those found on an isometric grid

with an isometric grid the basic shape of an equilateral triangle can be used to determine other angles

see potentially earlier work on 7 pins

later work can then focus on deciding upon and establishing (i.e. justifying) what various angles are - from a restricted set, to work towards establishing the interior angle sum for various polygons

the 'other' angle to make 360 degrees might also be of interest
'explementary' seems to be a (rarely used) term for this