| Name and Model Number | Léon Lalanne |
| Country of Origin | France |
| Date of Manufacture | circa 1850 |
| Front Scales | The slider is visible through two windows in the body of the slide rule. The upper window handles trigonometric functions. The lower window displays A,B,B and D scales in the normal nomenclature, and includes specialized gauge marks. |
| Back Scales | The slider is visible through a single window. Two pairs of C and D scales are provided. A wide range of gauge marks are also provided, in French, including parameters relating to molten metals and conversion factors for measurements new and old. |
| Scale Length | 247 mm (approx. 9.75”) |
| Type of Rule | Slide Rule |
| Construction | Cardboard and paper |
| Area of Use | Other |
| Comment | Probably used for metallurgy. |
| Rarity | RRRR |
| Donor | Collection of Trevor Catlow |
| Match Number | 77 |
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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. |