Patent
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Patent:US4251721
17.02.1981 Rathbun, Charles D. (1005 Mistletoe, Ft. Worth, TX 76126) : Pattern and threshold speed calculator
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Patent:US4251935
24.02.1981 Wright, Marvin A. : Perpetual calendar
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Patent:US4257174
24.03.1981 Presley, Wayman R. (RFD #1, Makanda, IL 62958) : Device for teaching counting
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Patent:US4262939
21.04.1981 Schoettle, Jr., Karl R. (1 Private Way, Strafford, PA : Slide chart manufacture
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Patent:US4268477
19.05.1981 Herzstark, Curt (P) Bna Augustin GmbH und Co : Apparatus for distribution of liquid test samples through various test
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Patent:US4272107
09.06.1981 Elbow, William T. (South Rd., Chilmark, MA 02535) : Tide time indicator
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Patent:US4272674
09.06.1981 Mutsumi Takahashi Toshio Uwabe Toshio Nagase Shosuke Sato Hideshi Matsuzawa Tokyo Keiki (P) Comp. Ltd. Totec Co. Ltd. : Check digit calculator
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Patent:US4282655
11.08.1981 Daniel Tinman : Cardiac axis calculator
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Patent:US4305323
15.12.1981 Graham, Bruce (P) : Harmonic Conversion Wheel
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Patent:US4306141
15.12.1981 Bailey, Joan F. (280 Alto Dr., Oak View, CA 93022), : Mechanical astrological calculating device
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Patent:US4307649
29.12.1981 Arthur Amos : Slide Rule for fretted musical instrument
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Patent:US4308449
29.12.1981 Kelley Clair S Us Army : Tactical nuclear Slide Rule
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Patent:US4308450
29.12.1981 Ausman, Robert K. (Long Grove, IL), Tucker, Hugh N. : Two-piece slide calculator for determining metabolic requirements and parenteral feeding dosages