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| 3819177 | Spiro | Jun 1974 | |
| 3972238 | Thatcher | Aug 1976 | |
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| 5217186 | Stewart et al. | Jun 1993 | |
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| 5460589 | Dunn | Oct 1995 | |
| 5472394 | Michaelson | Dec 1995 | |
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| Entry |
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| Power Systems, Product Catalog Fall/Winter 1997, Knoxville, TN, p. 5. |
| Power Systems, Product Catalog Fall/Winter 1998, Knoxville, TN, pp. 3 and 5. |