| Name and Model Number | Spirule by Walter Evans |
| Country of Origin | U.S.A. |
| Date of Manufacture | |
| Front Scales | Specialised Scales |
| Back Scales | |
| Scale Length | 29.2 cm |
| Type of Rule | Other |
| Construction | Plastic |
| Area of Use | Other |
| Comment | Used for addition of angles or multiplication of lengths of vectors.
The Spirule can also be used in plotting vectors or as a circular slide rule. |
| Rarity | RR |
| Donor | Collection of Rod Lovett |
| Match Number | 27 |
| Thumbnail |  |
| RR | = Rare -- 1 of 25 collectors has one; it may take a year to find an example in the marketplace. |
| RRR | = Very rare -- only very few known to collectors; may take several years before one comes up for sale. |
| RRRR | = Extremely rare -- a museum piece; unlikely that an example will ever come up for sale. |