| Name and Model Number | Lawrence Model Builders |
| Country of Origin | USA |
| Date of Manufacture | c 1950 |
| Front Scales | Prototype/Model (Imp, Metric), Prototype/ Model/ditto |
| Back Scales | None |
| Scale Length | 25 cm |
| Type of Rule | Slide Rule |
| Construction | Wood |
| Area of Use | Other |
| Comment | Model railway scale calculations. |
| Rarity | RR |
| Donor | Collection of Colin Barnes |
| Match Number | 82 |
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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. |