Full Details

Name and Model Number Keuffel & Esser
American Optical
Dr. Prince Refracting Rule
Country of Origin USA
Date of Manufacture 1920-1950
Front Scales Age in years, Dioptric Correction
Back Scales Instructions
Scale Length 48 cm (19 inches)
Type of Rule Slide Rule
Construction Solid boxwood or pearwood frame, no slider scales are logarithmic
Area of Use Technical
Comment Refracting Rule for eye examinations replaced by electronic gadgetry see JOS-v17-n2-2008-page28 Title: Dr. Prince's Refracting Rule Made by K&E
Rarity RRR
Donor Collection of Clay Castleberry
Match Number 374
(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.