Help in Rotating image to scale

Hi

ive got a problem ive been rotating my original image around in a circle to create a cool effect, yet i want to rotate it back around with the front but how do i do that and keep the same scale. i was measuring the top rotation of of a certain part on the car and bringing it to that each time to keep it the same but now i cant since its not symmetrical
in short terms I need "Gap a" to = "Gap b"
any advice welcome
thanks.

hi,
You can set registration point (center point) of your image and then rotate.

Press shift while rotating, you'll get a 15º rotation angle.
if 15 are not good for you, use the angle textbos on the options bar and enter your desired value.

With your original layer selected, do a free transform but hold Ctrl+Alt+T. Adjust your center point and hit okay. Now do a copy transform - Ctrl+Alt+Shift+T. You may need to play with your center point, but this is far easier than redoing your transform every single time.