Some visitors may use standard monitors and others may use widescreen monitors.

A standard monitor may have 1024x768, 1280x1024, 800x600, or the older 640x480; or some higher resolutions.

A widescreen monitor can have 1280x768, 1440x900, or higher resolutions.

A standard 1280x1024 and a widescreen 1280x768 could have the same centering left to right; however, top to bottom would not work for one or the other.