Editor's note: Please see an update to this tip titled Automatically Draw Arrowheads on Circles and Arcs.
Rotating Annotation (Tip #2123) from William J. Townsend is a good example of a dimensioning utility. Load the LSP file into AutoCAD and type RT1 to add a rotational arrow and arc to an existing circle or arc object in your drawing. When RT1 starts it asks you select an arc or a circle. Next, it asks for the direction point (end of the arrow tip). This angle is where the annotation for the rotation starts. Next, specify where the annotation is to be drawn relative to the input object (inside or outside). The distance between the original object and the annotation is half the dimension text height. It then requests the extent of the rotation (full or partial) and the direction (clockwise or anticlockwise). An annotation based on the input parameters is then drawn on the Rotation layer. This routine is handy for anyone who needs to show the rotation of a shaft (represented by a circle) or some other mechanical device.