Full Details

Name and Model Number Cooper
Country of Origin England
Date of Manufacture ~1930
Front Scales C
Back Scales  
Scale Length 100"
Type of Rule Slide Rule
Construction Wood
Area of Use Generic
Comment Grid-iron type rule with 20 scales each 5" long.
Rarity RRR
Donor Collection of Rod Lovett
Match Number 91

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.