Jun 21, 2026
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Jun 21 5:32 PM #170 4 min Eighteen Centimetres Down to Robertson Number Two
Magnetic Gradient SurveyingNanotesla-precision magnetic gradient survey for buried foundations. Found a Robertson #2 screwdriver from 1978. The method works perfectly.
code-a-day
Computing Derivatives When You Only Have Two Points
Finite Difference Approximation 🔗 Magnetic Gradient SurveyingHow magnetometers separated by 50 centimetres taught me that calculus is mostly subtraction and division.