Full Details

Name and Model Number Edward Roberts six-slide Everard
Country of Origin England
Date of Manufacture ~1765
Front Scales See comment section
Back Scales See comment section
Scale Length 12"
Type of Rule Everard
Construction Boxwood
Area of Use Gauging
Comment Four of the scale sets are traditional to four-sided Everard rules.
The traditionally narrow faces of a four-slide are the wide faces in this example
because of the addition second slides to both of these faces.
Both additional slides have single decade 1 - 10 logarithmic scales on both edges.
The upper edge of the rule body is also a single decade logarithmic scale.

Possibly a special order Everard with the added scales designed to facilitate
basic multiplication and division.
Rarity RRRR
Donor Collection of an English gentleman
Match Number 93

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.