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The dial is north-up — the red tick at the top is true north, always. The green line is the strike of the plane you are measuring and the short barb points down-dip. It is not a compass needle.
Lay the phone flat on the plane. iPhone needs permission — tap Start Sensors. Metal, vehicles and magnetite corrupt a magnetic heading.
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Answer only what you can. Every question you skip is fine — it just leaves more possibilities open, and the app will tell you what would narrow them.
These are the readings you attached to stations — not a demo set. When the poles spread onto a great circle instead of clustering, the engine names the fold and gives you its axis.
This is a straight-line bearing, not a retrace. In real terrain the straight line can cross a cliff. Use it with the ground in front of you, never instead of it.
Dr. Eleanora “Norrie” Robbins. American geologist. Research geologist with the United States Geological Survey from 1967 to 2001, and later adjunct faculty at San Diego State University.
In 1964 she went to Tanzania with the Peace Corps and worked as a field geologist for the Geological Survey there. Her research spanned palynology, geomicrobiology, iron formations and the chemistry of drainage from disturbed ground. After retiring she spent twenty-five years teaching outdoor science to Kumeyaay, Luiseño, Cupeño and Cahuilla children.
She carried the field to people the field left out, for sixty years. This app is free for the same reason.