| 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 |
| Thumbnail (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. |