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Magnetic distance and direction measurements from a first borehole to a second borehole
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Tool face orientation system for drilling boreholes
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Tracking system for drilling boreholes
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Two coil guidance system for tracking boreholes
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Drillstring alternator
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Elongated cross coil assembly for use in borehole location determination
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Elongated cross coil assembly for use in borehole location determination
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Earth magnetic field measurements with electronically switched current in a source loop to track a borehole
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Single solenoid guide system
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Elongated coil assembly for electromagnetic borehole surveying
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Two solenoid guide system for horizontal boreholes
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Relative drill bit direction measurement
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Electromagnetic borehole surveying method
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