V is the vertex, P1 and P2 points along the two arms, and RAD the radius at which the dimension arc is struck. The label is otherwise the measured angle and the degree symbol.

The angle measured is the one from the first arm to the second going counter-clockwise, so giving the arms the other way round dimensions the explement instead. That is the choice being offered, not an ambiguity: a corner and its outside both get dimensioned on real drawings.

See also: diam, radius, draw.symbol

Source Code: draw.Drawing