The HMC5883L magnetometer. This component (a small chip) HMC5883L, produced by Honeywell, bases its operation on AMR (Anisotropic Magnetoresistive) technology and allows you to be able to measure both the direction and the magnitude of the earth's magnetic field.
The magnetic field strengths are the total magnetic field strengths in nanoteslas. The angle shown in parenthesis is angle of the magnetic field downward direction. The influence of the downward tilt on the fast E1 pulse is quite complicated, but when there is less downward tilt, the intensity of the EMP tends to be more symmetrical around the detonation point.
A compass is nothing more than a tiny magnet suspended such that it can freely rotate in response to a magnetic field. Like all magnets, a compass needle has a north pole and a south pole that are attracted and repelled by the poles of other magnets.