It would be good to provide Plane X,Y,N rotation options to 3d Angle tool.

The user would select a Face and be presented a snap-enabled triad widget on the Face. This is to allow the user to select edge or define a vector on the Face for the rotational axis. The widget's second leg would define the starting vector for measuring the rotational angle. Anti-clockwise +ve. Right hand rule.

If the second part's Vertex is selected, its projection onto the Face will be used to calculate its angle.

If the second part's Edge is selected, its projection onto the Face will be used to calculate its angle.

If the second part's Face is selected, and its projection does not form an edge on the Face, the user will be asked to plave a triad on the second Face.

See previous discussion. Cases 2&3.