Full Details

Name and Model Number Burt's rule
Country of Origin U.K.
Date of Manufacture ~1895
Front Scales Coggeshall variant
Back Scales Tables of weight, railway rates, and wood measure
Scale Length 11"
Type of Rule Rule
Construction Boxwood and brass
Area of Use Other
Comment A 2-foot, 2-fold rule for transport using the railways.
Burtís rule, with its very idiosyncratic collection of tables
and measures, and a patent that was never awarded, is probably
the rarest of the 2-2 slide rules

Rarity RRR
Donor Collection of an English gentleman
Match Number 39

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.