turn on an axis

It may sound like a lot of effort just to achieve pleasing aesthetics, but when you're using the sun as your primary source of heat and electricity, which is true in some advanced sustainable building techniques, it starts to make sense.Structures that turn on an axis to follow the sun aren't new.

To measure the difference between the longitudinal co-ordinates of two objects by means of a graduated circle the instruments must turn on an axis parallel to the principal axis of the system of co-ordinates, and the plane of the graduated circle must be at right angles to that axis, and, therefore, parallel to the principal co-ordinate plane.