The rotation angle is the base physical quantity
In this paper, based on a careful analysis of the concepts of "rotation angle", "angular displacement", "plane angle" and "dimensionless quantity", it is concluded that the angular displacement and rotation angle are different physical dimensional pseudo vector quantities, measured in units of plane angle. It is indicated that the natural unit of plane angle is a revolution (rev), but not an adopted in the SI radian (rad). We present evidence that the rotation angle is the base physical quantity. Shown an imperfection of the existing in the mechanics classification of types of mechanical motion and proposed another classification of forms of mechanical movement, which explains why the rotation angle and angular displacement are different physical quantities. Concluded about what should be the units of physical quantities characterizing the rotation of the body and its movement along a curved orbit.