Rarity designations in English Silver Coinage?

[stackcal]

Just received the latest (6th) edition of English Silver Coinage and am puzzled by some of the rarity designations. There are R and C usually with a following superscript, R³, C², etc. I assume that R means rare and C means common, and the larger the number following R means more rare. But does a larger number following C mean more or less common, i.e. is a C² coin more or less common than a C³ coin? What do C and R mean when there is no superscript? What do N and S mean? Haven't found a key in the book. Maybe I missed it.

Book has a ton of info, but could use an introductory chapter to explain symbols, references, abbreviations, etc. Glad for any help.

[HawkHybrid]

English Rarity Scale - from The English Silver Coinage from 1649 by Seaby & Rayner. 
R7 - only 1 or 2 examples known 
R6 - 3 - 4 
R5 - 5 - 10 
R4 - 11 - 20 
R3 - Extremely Rare 
R2 - Very Rare 
R - Rare 
S - Scarce 
N - Normal, neither scarce nor common 
C - Common 
C2 - Very Common 
C3 - Extremely Common 

 

HH

[stackcal]

Many thanks, Hawk.  Surprising they didn't put the definitions in the newest edition.