Full Details

Name and Model Number Lawrence Model Builders
Country of Origin USA
Date of Manufacture c 1950
Front Scales Prototype/Model (Imp, Metric), Prototype/ Model/ditto
Back Scales None
Scale Length 25 cm
Type of Rule Slide Rule
Construction Wood
Area of Use Other
Comment Model railway scale calculations.
Rarity RR
Donor Collection of Colin Barnes
Match Number 82

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.