Can someone tell me what the diameter of the meter is in degrees for the standard 50mm lens on a Nikon F3 HP?

It appears to be sensitive within approximately the split screen area, and secondarily sensitive within the prism focus ring around the split screen focus.

My son is using this camera in a photo class he is taking. I am trying to explain to him the difference between my 1 degree spot and the angle of sensitivity of the camera.

Thanks for the help