A version 2 avar table lets an axis move the others: in the second font, full weight also narrows the width and a narrow width also makes the weight heavier, so the same font-weight and font-stretch settings read differently than in the plain font of the same design.
ABAB plain font, font-weight: 900 | ABAB avar 2 font, font-weight: 900 |
ABAB plain font | ABAB avar 2 font |
In vertical text each glyph advances by its vertical advance, which follows the axes through VVAR (or, without it, the phantom points of gvar): the heavier the weight, the longer the column.
ABCABC font-weight: 100 | ABCABC font-weight: 400 | ABCABC font-weight: 900 |