I am a relatively new user the ProE and having a bit of difficulty creating datum planes at angles to others. All other datum function seem to be working but I can't bring up the contents/index help page inside the program!
The procedure explained by Xcad is best. This procedure is used when the feature created need to be patterned around the axis. Because of this the New Datum plane is created. Important point is the NEW DATUM PLANE CREATED IS DURING THE FEATURE CREATION. I.E., DATUM ON FLY. So that the angle can be used as the dimension in rotational patterned.