You can define the rotation angle by dragging the selected objects:
Extra instrumentation is drawn to help you rotate the objects; the angle of rotation displayed, a line is drawn from the selected objects to the rotate axis marker, and a circle is drawn around the rotate axis from the position the line touches the objects.
The line is half solid and half dashed. If the cursor is over the solid part when you drag the objects , the rotation angle changes by increments of 15. With the cursor over the dashed part , the angle changes by 1. If you move the cursor so that it lies outside the circle , the angle changes by 0.1.
The circle shows the rotation path around the axis.