The macroscopic view
•The NMR experiment measures a largenumber of spins derived from a huge number of molecules. Therefore, we now look at the macroscopic bevaviour.
•The sum of the dipole moments of all nuclei is called magnetization. In equilibrium the spins of I=1/2 nuclei are either in the a  or b-state and precess about the axis of the static magnetic field. However, their phases are not correlated.
•For each vector pointing in one direction of the transverse plane a corresponding vector can be found which points into the opposite direction:
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