| Name and Model Number | Halden Calculex Desk Model |
| Country of Origin | England |
| Date of Manufacture | c. 1918 |
| Front Scales | L, A [ B, C(Square Root of B) ] |
| Back Scales | Degrees A [ BI, N(Cube Root of BI) ] |
| Scale Length | 10.2" (26 cm) |
| Type of Rule | Disc |
| Construction | Metal with paper scales and glass windows. |
| Area of Use | Generic |
| Comment | Large scale (5” diameter) version of the popular Halden Calculex.
Double sided pocket watch calculator with front and rear rotatable inner scale discs. Front and rear glasses have inscribed cursor lines and are rotatable. Handles on the center hub aid in turning the inner discs. |
| Rarity | RR |
| Donor | Collection of Dr. Paul J. Tarantolo Jr. |
| Match Number | 30 |
| 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. |