| Name and Model Number | Simpson’s rule |
| Country of Origin | UK |
| Date of Manufacture | c1905 |
| Front Scales | Noble scales and tables |
| Back Scales | Routledge engineering with gauge points inc Aluminium, conversion factors, no steam gauge points |
| Scale Length | 11” |
| Type of Rule | Other |
| Construction | Boxwood & German silver |
| Area of Use | Other |
| Comment | A 2-foot, 2-fold rule used in Engineering.
Abraham Simpson’s slide rule from sometime in the early 20th century is a strange mixture of Routledge engineering and Noble’s designs of engineering 2-foot, 2-fold slide rules. Engineering calculation is carried out on the one side; the second allows weight of steel sheet etc to be done as on a Noble rule. Simpson included some calculations not possible on the other two designs. Alfred Harper of Birmingham (1900 – 1925) is not a well known maker, the factory burned down in 1925. |
| Rarity | RRR |
| Donor | Collection of an English gentleman |
| Match Number | 66 |
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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. |