Based on Bohr-Sommerfeld model the quantization of magnetic flux through the electronic orbits is investigated together with its dependency on additional sources of magnetic fields. The additional magnetic field causes changes of the angular momentum and hence shifts of the energy of the atomic levels. This effect is investigated for the cases of the Zeeman effect, where the source is an external homogeneous magnetic field, and the hyperfine interaction, where the source is the field of the magnetic moment of the nucleus. A model for the handling of the different angular momentum contributions is discussed for which the energy shifts due to Zeeman effect and the magnetic dipole contribution to the hyperfine interaction can be reproduced quite well. The meaning of 'spin', however, changes within this approach drastically. The unusual Land g-factor of the electron is discussed to be the result of a reduced ground state angular momentum of the electron in combination with the field of the magnetic moment of the electron rather than an intrinsic property of the electron.