| Name and Model Number | Controller Calculator KG, prototype 30 cm circular slide rule |
| Country of Origin | Germany |
| Date of Manufacture | 1960s (estimated) |
| Front Scales | C [D A K ] |
| Back Scales | Weights and measures conversion tables |
| Scale Length | 82 cm |
| Type of Rule | Disc |
| Construction | Aluminum alloy, celluloid cursor |
| Area of Use | Generic |
| Comment | This is apparently an unreleased prototype for a 30 cm diameter model that extends
the familiar range of Controller circular slide rules (comprising 7.5, 11 and 20 cm units). For details see https://www.nzeldes.com/HOC/Controllers.htm |
| Rarity | RRRR |
| Donor | Collection of Nathan Zeldes |
| Match Number | 414 |
| 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. |