Parallax
This is a type of perspective. Where you're looking FROM changes what you see where you're looking TO. It can create distortion.
This picture illustrates why. So, keep you head still when using your reference points, or judging position. If you do move it, be aware of the effect that has on what you see, and account for it. More positively, to tell how far your bonnet is from a wall, move your head a little side-to-side and see if the end of your car appears to move sideways compared to the wall. If it doesn't... you're very close! |