The metrics I use relate to how often a coin type appears on the international markets Once a decade or less
, and it is of major importance when one appears - excessively rareOnce every two or three years
and there's a buzz about the sale - extremely rareAbout once a year
; in a given two or three month catalog/internet lookahead there might be none or one - very rareSeveral times a year
; if one searches one can usually find an example or two in a 3 month interval - rareOne or two examples now
, in an internet search and/or including upcoming auctions - scarceA range of examples are available
at fixed-price and in upcoming auctions - commonMultiple examples
are available at fixed-price and in upcoming auctions - very commonYou have to wade through bucketfuls
of this type to find an interesting coin - extremely common
(this is calibrated around Roman Republican
silver which is a popular collecting area where very rare coins are virtually guaranteed to get listed in a major auction: for less popular areas such as Republican bronzes, even genuinely rare types are often ignored by sellers and languish in pick-boxes; thus frequency of appearance in proper auctions is less than the rarity justifies)
I have written some words on the concept of rarity here:http://andrewmccabe.ancients.info/Auctions.html#jump
Warren Esty has written better words here:http://esty.ancients.info/numis/rarity.html
From Warren's site: here is Glossary of eBay terms (tongue in cheek): "not in Sear"
It is unlisted in Sear's book, so I can't give a Sear number. (I hope you think this makes it rare and valuable.) [Of course, RIC lists thousands of varieties not in Sear, so it doesn't really mean much at all.] "r2" or "very rare"
RIC lists it as "r2" [This is almost meaningless for late Roman coins.] "Unlisted"
I have only one book and its not in it. "The first one I've seen"
I've been collecting for a year, have almost no reference works, and have not yet seen this [although experienced collectors have seen 50 examples]. "Van Meter Value Band 2"
A more-expensive type. (I hope you don't know that this late Roman copper type has been pouring out of the Balkans since the iron-curtain came down [after van Meter wrote his book] and they immensely more common than they used to be and are going for 1/4 what they sold for when van Meter wrote his book.) "unpublished"
I have several of the major references and its not in them. [But most of them are 20 or more years old and who knows what has been published since then?]