Full Details

Name and Model Number Favor, Ruhl & Co.
SR108 & MD7
Country of Origin USA
Date of Manufacture c. 1945
Front Scales K A [ B S T C ] D DI
Back Scales [ L C2 C1 ] D1 D2 D
Scale Length 12.5 cm
Type of Rule Slide Rule
Construction Celluloid laminate over wood duplex slide rule 18-cm long; with plastic cursor.
Area of Use Generic
Comment Open frame extended scale duplex slide rule with C1, C2, D1 & D2 scales extended, giving an effective scale length of 25 cm on a 12.5 cm slide rule.
Made by Charvoz-Roos for Favor, Ruhl & Co. Model Nos. SR108 & MD7 both appear on slide rule.
Also made for Frederick Post Co. during WWII and labeled as Post's No. 1442.
Rarity RR-RRR
Donor Collection of Ed Chamberlain
Match Number 185
(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.