Fred Michaelson writes:

Leave it to Q. David Bowers to recognize the need, and develop a method that could be used for any series, and any rarity. In fact, this can be used not only with coins, but with virtually anything when rarity, scarcity, or availability was important. Bowers developed The Universal Rarity Scale (URS), which as its name implies, is universal for any coin or item. Bowers outlined his scale in the June 1992 issue of The Numismatist. It has already been adopted by many writers and catalogers, including exclusive use in The Cherrypickers' Guide.

The URS is a reasonable mathematical progression. One does not need to have a copy with him or her to be able to determine a correct URS. Just simply remember the easy progression.

The Universal Rarity Scale

URS‑0: None known
URS‑1: 1 known, unique
URS‑2: 2 known
URS‑3: 3 or 4 known
URS‑4: 5 to 8 known
URS‑5: 9 to 16 known
URS‑6: 17 to 32 known
URS‑7: 33 to 64 known
URS‑8: 65 to 125 known
URS‑9: 126 to 250 known
URS‑10: 251 to 500 known
URS‑11: 501 to 1,000 known
URS‑12: 1,001 to 2,000 known
URS‑13: 2,001 to 4,000 known
URS‑14: 4,001 to 8,000 known
URS‑15: 8,001 to 16,000 known
URS‑16: 16,001 to 32,000 known
URS‑17: 32,001 to 65,000 known
URS‑18: 65,001 to 125,000 known
URS‑19: 125,001 to 250,000 known
URS‑20: 250,001 to 500,000 known
Etc.

As you can see by the Universal Rarity Scale (URS), the mathematical progression is simple, and can be applied to any item as an indication of rarity. In addition, the scale, being simple, does not require memorizing the scale, as one can figure what population a URS number indicates.

To read the complete article, see:What The Numbers Mean(www.coinresource.com/articles/dies_variities_error_numbers.htm)

To read the earlier E-Sylum article, see:WAYNE'S NUMISMATIC DIARY: JUNE 16, 2013(www.coinbooks.org/esylum_v16n25toc.html)