| Name and Model Number | IWA Model #1638 System Wern |
| Country of Origin | Germany |
| Date of Manufacture | c.1968 |
| Front Scales | M N D A [ B ] T S [ r ] p a [ b C c V ] LL |
| Back Scales | None |
| Scale Length | 51 cm |
| Type of Rule | Disc |
| Construction | Thin plastic square scale disk (21-cm x 21-cm) with second scale disk (16.3-cm dia.) and transparent cursor. |
| Area of Use | Generic |
| Comment | Designed for "Direct Reading" of the "Decimal Point" location. Follows the 1968-patented design of C.R., G.H. & L.A. Wern. The A & B scales run 8-decades from 10 E-02 to 10+E06. The LL scale runs from 1.001 to 10+E40. Includes other special scales. Guide to scales is printed on the cursor. Introduced in Germany in 1968, just before the end of the slide rule era. Does not seem to have gained much traction. Most known examples appear unused, coming from unsold inventory. Last of the known "Decimal Keeping" slide rules. |
| Rarity | RR |
| Donor | Collection of Ed Chamberlain |
| Match Number | 179 |
| 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. |