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Message:: [QUOTE="Conder101, post: 1865484, member: 66"]The problem with Bower's URS is that it really ISN'T an improvement over the Sheldon Rarity Scale.  The Sheldon scale has 8 levels with 8 being the rarest and 1 the lowest.  By the time you get down to an R-1 you are looking at a population of over 1,500 specimens estimated and once you try to go beyond that any real population estimates are just wild guesses.  So there is not much point in trying to make estimates. The URS is an open ended scale starting at 1 for the rarest and increasing with each increasing number  The thing is once you get past URS 11 you are once again dealing with populations that are no better than wild guesses.  So anything past URS 11 is pretty much pointless. This means for practical rarity you have the old 8 point scale and the new 11 point scale.  Not really any great improvement and hardly in indication that the old scale is obsolete.  Especially when you consider that the Sheldon R-8 needs three numbers in the URS scale, 1,2, and 3.  URS 4 and 5 fairly well matches Sheldon R7, Urs 6 and Sheldon R-6 are fairly equal. Sheldon R-5 is URS 7 and 8 etc.  Some might say the URS has "finer" divisions in the population counts, but the Sheldon Scale allows for that as well by using + to indicate a population in the scarcer third of the range and a - for the more common third of the range. In short the URS scale has no real advantage or improvement over the Sheldon Scale.[/QUOTE]