"................foreshortening, perspective, variations in the immediate landscape. I guess some peoples visual acuity can account for, and adjust accordingly to compensate for natural illusions. We all have to remember that there are some "Rain Man" type people out there who's brains and powers of perception are far more advanced than those of the rest of us. It would seem that our lovely spanner is one of these suitably advanced people.
Aircraft registrations are INTENTIONALLY large enough to be read from distances further than the limits of Rule 5. Depending on the type of vehicle spanner was driving, the shape of most windscreens dictate that objects above vehicle roof level must be a considerable distance away, horizontally, before they can be seen from behind the drivers seat. This horizontal distance then introduces several "curve-balls" to anyone bold enough to believe they can accurately measure the height/altitude of the object being viewed. Some are mentioned above..........
Spanner is competent enough to compensate for any induced errors and determine ACCURATELY; the height, track, etc of the aircraft in question; whilst driving SAFELY in low visibility (spray from rain!!!) from the comfort of his driving seat.
Go figure!!
LFB.