Each axis spans the range the 453 bookshelves in the catalog actually cover, so equal distance means equal difference — and for cone area and the two frequencies, which are read as ratios, equal distance means equal ratio. The dashed inner ring is where the scale starts, not zero. Ranked within a class because a bookshelf measured against floorstanders is feeble on every axis for the single reason that it is a bookshelf. Cone area is summed from the drive units — no maker publishes it. Bass and treble reach are quoted to different tolerances and only 56% of the catalog says which, so read those two axes as approximate. The grey outline is the median of this speaker's own class, the 381 passive bookshelves — same type, same side of the active/passive line, which matters because the two halves are not the same product: the median active bookshelf carries 155 cm² of cone against the passive median's 219. Median rather than mean, because a handful of very large cabinets would drag a mean above most of the class it claims to describe. Not shown: Bass reach, Treble reach — the maker publishes no figure.