True, I assumed single-layer as billy isn't open-backed and I prefer seeing all my books. Also billy seems a bit short for two layers to be comfortable and not risk damaging books, even with small-ish paperbacks.
The exact number of Billies may have been a bit different but the discussion quickly shifted to the ubiquity of the Billy and what it said about the global economy and how easily we adopt custom standards.
I remember being surprised by that new unit but also astonished by the fact that I instinctively understood what he meant.
