Full Details

Name and Model Number Dempster Rotarule AA
Country of Origin U.S.A.
Date of Manufacture 1972
Front Scales K, A, D [C, CI, CIF, S, C, ST, T, CT, G (2 scales), B, F/i]
Back Scales L, LL%, LL1, LL2, LL3, C [V1, V2, DLL, D]
Scale Length 13.0 cm diameter
Type of Rule Disc
Construction Plastic
Area of Use Generic
Rarity RR
Donor Collection of Rod Lovett
Match Number 18

RR = Rare -- 1 of 25 collectors has one; it may take a year to find an example in the marketplace.   
RRR = Very rare -- only very few known to collectors; may take several years before one comes up for sale.   
RRRR = Extremely rare -- a museum piece; unlikely that an example will ever come up for sale.