To rotate a shape:
To rotate a shape by a fixed amount: Click to select the shape. On the Shape Format tab, in the Arrange group, click Geometry button. In the Angle box, type the angle you want, and then press Enter.
Tips: As you rotate shape, the angle of single dragging depend on the distance of the mouse point and the shape pin, the distance is larger the angle is littler. The angle of single dragging may be 15 degree, 10 degree, 5 degree, 1 degree, 0.1 degree. So if you want rotate shape to a precise angle, you should drag the mouse enough distant from shape's pin.