text: Any free system with a constant gyromagnetic ratio, such as a rigid system of charges, a nucleus, or an electron, when placed in an external magnetic field  (measured in teslas) that is not aligned with its magnetic moment, will precess at a frequency  (measured in hertz), that is proportional to the external field:
  For this reason, values of , in units of hertz per tesla (Hz/T), are often quoted instead of .