Full Details

Name and Model Number Johann Faber
Country of Origin Germany
Date of Manufacture c 1880
Front Scales A/B,C/D
Back Scales S,T
Scale Length 125 mm
Type of Rule Slide Rule
Construction Mahogany/celluloid
Area of Use Generic
Rarity RRR
Donor Collection of Colin Barnes
Match Number 81

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.