Full Details

Name and Model Number Carrett’s rule
Country of Origin U.K.
Date of Manufacture ~1865
Front Scales Routledge variant
Back Scales Tables of general engineering facts and figures
Scale Length 11"
Type of Rule Rule
Construction Boxwood and brass
Area of Use Technical
Comment A 2-foot, 2-fold for Engineering calculations.
Carrett’s rule has own special collection of different
scales and tables, examples are rare, this particular
one made by \Rabone is unusual in having a boxwood slide.
It too is amongst the rarest of the 2-2 slide rules.
Rarity RRR
Donor Collection of an English gentleman
Match Number 40

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.