To rotate by a precise factor, similar to the "Scaling the Model by a Factor" topic, do the following:
From the Graphics Modes toolbar, select the 2D Rotate Mode icon .
In the Graphic Display window, press Shift and then right-click to show a small dialog box.
Type the angle (in degrees) into the Angle of part coordinates X box.
Click OK to closes the box and perform the 2D rotate of the part in the Graphic Display window.