Full Details

Name and Model Number Charpentier Calculimetre
Country of Origin France
Date of Manufacture Before 1900
Front Scales C, [D], [R]
Back Scales L, S, T
Scale Length 5.9 cms Diameter
Type of Rule Disc
Construction Steel and Copper
Area of Use Generic
Rarity RR
Donor Collection of Rod Lovett
Match Number 17

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.