ORIGINAL: Tall Paul
I have the Nye drawing... all this other stuff is just talk.
7 minutes of angle seems too small to be measureable, or even a design requirement, considering the time period., or it's an attribute for the particular plane measured.
There's certainly no aerdynamic reason for such an infinitesimal deviation.
No, it's not just talk. My data is from a 1943 workshop manual for the Spitfire Mk. V that I happen to own. I have no idea why Supermarine bothered to indicate such a small angle, but some draughtsman thought it was important enough to produce a drawing illustrating this.
As far as I know the wing twist (2.5° or 2°30') stated for the Spitfire wing does not include the wing tips. Depending on the intended application three types of wing tips were used, normal, clipped and extended.
/Red B.