When you use this button, TAD would try to rotate the current object (or current set of selected objects) precisely. However for this command to work, you would need to ensure that the angle is given

But where to give that angle? Press F10 to invoke the HeadsUp Commandline and give the angle value in there. Angles are measured in degrees. A positive angle would give a counter-clockwise rotation

All rotations are centred around the architect