Full Details

Name and Model Number Small's Pocket Calculator
Country of Origin U.S.A.
Date of Manufacture ~1918
Front Scales C, D // 6 ins, CI, S
Back Scales L, R1, R2, SRT
Scale Length 4.9 cm diameter
Type of Rule Disc
Construction Metal
Area of Use Generic
Rarity RRR
Donor Collection of Rod Lovett
Match Number 26

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.