Full Details

Name and Model Number E.D. Co. 6 & 10 Inch
Proportional Divider
Country of Origin Germany
Date of Manufacture First half of 1900's
Front Scales Small dividers scale of lines, scale of circles -- large divider has scales for proportions and has a vernier.
Back Scales None
Scale Length 15cm (6 inch) & 25cm (10 inch)
Type of Rule Instrument
Construction Fine machine work on nickel steel, or German silver
Area of Use Nautical
Comment Primarily used for navigation, astronomy, or proportional calculations. There is an article in OS Journal volume 17, No 2, from 2008, by David D McFarland that explains proportional dividers as mathematical calculating tools for finding square roots and solving other math problems.
Rarity RR
Donor Collection of Clay Castleberry
Match Number 355
(Click Picture for Details)

In conjunction with our 'donors' we assign a rarity rating to each item, based on the system devised by Herman van Herwijnen
(1929 - 2004), renowned Dutch collector, author, and creator of Herman's Archive, a collection of 5,000 slide rule images on CD.
• RR = Rare - 1 of 25 collectors has one; it may take a year to find an example in the marketplace.
• RRR = Very Rare - only a few known to collectors; may be several years before it comes up for sale.
• RRRR = Extremely Rare - a museum piece; unlikely that an example will come up for sale.