What is the difference between auto (multiple of 640x528) and a preset resolution?

[Nerrel]

I had assumed auto (multiple of 640x528) would just select the appropriate resolution for your performance level (1x, 2x, etc) and nothing more. In some games that's exactly what happens, but in others I notice a difference between auto and the preset resolution options, both in terms of picture quality and performance.

For instance, in Skyward Sword auto leads to a frame rate and visual quality distinctly different than either the 3x or 4x settings, falling somewhere between the two (effectively 3.5x). Can someone explain to me how this setting works, and why it provides a different result than just selecting a set resolution from the list?

[RachelB]

It depends on your window size, kind of like auto (window size), but only in multiples of 640x528.

[NaturalViolence]

Are you sure you didn't have it on auto window size?

[Nerrel]

Yep. I noticed the framerate and resolution differences with the game windowed or in fullscreen; in fullscreen, it runs about 39fps on 3x, 34fps on Auto(multiple), and 29 on 4x.