It's an entire font set that consists of nothing but numbers. They take inspiration everywhere from the US currency to Hungarian banknotes to Soviet house numbers. It's quite an interesting concept. In Deuce, they take their inspiration from the numbering on playing cards, that is a very recognizable numbering form. They are really quite nice, and I wouldn't expect anything less coming from Hoefler & Frere-Jones. They have created some of my favorite fonts. The only one that has a little issue in legibility is Dividend. I love the concept of the numbering and the original use for it was quite ingenious. However when then numbers get into the fractions and smaller sizes they get harder to read. They did a nice job of trying to fix it but there are still some issues of legibility.
This is exactly like the bitmap font project at the end of Type1. We were given a 10x10 grid and had to pick an object to use to create a type face within that 10x10 grid. Granted they had more leeway in the creation of their font, its the same basic principles. They had dots, I had push pins. Taking a simple shape(in their case dots) and create a legible font out of that one shape.
SOURCES: HOEFLER & FRERE-JONES.