| Name and Model Number | Carrett’s rule |
| Country of Origin | U.K. |
| Date of Manufacture | ~1865 |
| Front Scales | Routledge variant |
| Back Scales | Tables of general engineering facts and figures |
| Scale Length | 11" |
| Type of Rule | Rule |
| Construction | Boxwood and brass |
| Area of Use | Technical |
| Comment | A 2-foot, 2-fold for Engineering calculations.
Carrett’s rule has own special collection of different scales and tables, examples are rare, this particular one made by \Rabone is unusual in having a boxwood slide. It too is amongst the rarest of the 2-2 slide rules. |
| Rarity | RRR |
| Donor | Collection of an English gentleman |
| Match Number | 40 |
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| 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. |