Major vs. Mixolydian

The first of these is the major scale - Ionian, in Greek-mode terms - and both start on C.

The wheel makes the difference positional rather than verbal: the seventh-degree wedge sits one wedge further counterclockwise in Mixolydian, and the spoke drawn from the center recolors to the interval that degree now forms with the tonic. Everything else on the two wheels is identical.

That single degree is the difference between a leading tone that pulls back to the tonic and a flat seventh that doesn't - the note that gives Mixolydian its bluesy, dominant-seventh pull instead of the major scale's settled resolution. Reading it is one thing; the difference is much more obvious held under a drone, which is what the links under each figure are for.