What rarity scale does CONECA use?

I was on the CONECA website looking at the listings for Buffalo nickel RPMs. In the rarity section it lists a number. I know there are a couple different rarity scales and am curious as to which scale CONECA uses. If a coin has a rarity of 6 according to the website, how many are they estimating for a particular coin? Thanks for the info.
Chris
Chris
Chris
My small collection
Want List:
'61 Topps Roy Campanella in PSA 5-7
Cardinal T206 cards
Adam Wainwright GU Jersey
My small collection
Want List:
'61 Topps Roy Campanella in PSA 5-7
Cardinal T206 cards
Adam Wainwright GU Jersey
0