Judd separated rarity into eight classes: Rarity-8 (2 or 3 known); Rarity-7 (4 to 12 known); Rarity-6 (13 to 30 known); and so on. Market participants have since particularized the most highly prized rarities into High and Low, such as in High Rarity-7; some take another tack and add a plus or minus sign, as in Rarity-2+. (Thus, in a sub variety of 1793 large cent we might find this enlightening description: "1793 Wreath. Vine and bars edge. Sheldon-9b. Rarity-4+."
It should be understood that rarity numbers using Judd's system derive from educated guesses, i.e., participant experience.
Following the debut of slabbing came so-called grade-rarity, the second method of determining a coin's rank, and much more amenable to price manipulation. Grading services compile large pools of data. Their published census figures for each grade give a helpful, though oftentimes skewed look at the rarity of various coins in various conditions. Naturally, this latter system leaves something to be desired, but who has anything better to offer? It fails to include coins from competing services, or coins that have been submitted for grading more than once; worse, it ignores raw coins. And it fails to take into account the observed fact that many people dispute a coin's assigned grade. But, what the heck! See pop.
Forerunners to rounds were rectangular one-ounce bars that hit collectors' fancies beginning in 1972. This earlier craze got out of hand when untold thousands of types were stamped out and sold to unwitting guppies at delightfully obscene markups. As with all such fads, this one imploded and left investors counting up their losses.
For a time in the mid-1980s, five-ounce rounds were all the rage. Then, in the 1990s, came government mints issuing twelve-ouncers as well as kilo rounds in such metals as gold, platinum, palladium, and, it is rumored but not verified, protactinium. In the January 18, 1993 issue of Coin World is reported the sale of a 5-kilogram (11-pound) gold round or Panda of China. "The coin was reported sold for $147,000" to an American buyer. (Are hundredweight rounds next? And how about plutonium?)