This rule was designed to calculate the cost of producing steam for boilers.
| Slide rules HOME page | COLLECTION | SPECIALISED RULES |
| Make | Not given (possibly Unique). Made for Vickers-Spearing Boiler Co. |
| Model | Calculations of boiler efficiency and energy costs. |
| Notes This rule was designed to calculate the cost of producing steam for boilers.
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| Manufacturing date | Copyrighted in 1923. Probably produced about that time. |
| Length | Not applicable |
| Material | Plastic on wood |
| Scales | Not applicable |
| Cursor | Glass and brass (not shown) |
| Documentation | None. Instructions and background are given here. |
| Condition | Good working order |