Patent classifications
E
FIXED CONSTRUCTIONS
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E21
EARTH OR ROCK DRILLING; MINING
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E21B
EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
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47/00
Survey of boreholes or wells
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E21B47/02
Determining slope or direction
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E21B47/022
of the borehole, e.g. using geomagnetism
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E21B47/0228
using electromagnetic energy or detectors therefor
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E21B47/0232
at least one of the energy sources or one of the detectors being located on or above the ground surface
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