It is usual to interpret the measured magnetic field in terms of the electrical currents that cause it.
The magnetic field vector, dB, due to a current, I, flowing along the vector element, dl, at a position, r,
is given by the BiotSavart law.
Thus we see that the magnetic field perturbation is perpendicular to the direction of the electrical current (Idl) and to the position vector of the current element (r). The magnetic perturbations caused by three simple current systems can be helpful in magnetometer interpretation:

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