A "Compound Plane Angle" is a compound measure of plane angle in degrees, minutes, seconds, and optionally millionth-seconds of arc.
Applicable units are those of quantitykind:PlaneAngle
http://standards.buildingsmart.org/IFC/DEV/IFC4_2/FINAL/HTML/link/ifccompoundplaneanglemeasure.htm
A "Compound Plane Angle" is a compound measure of plane angle in degrees, minutes, seconds, and optionally millionth-seconds of arc.