Value for the gyromagnetic constant

The International Council for Science: Committee on Data for Science and Technology adopted an updated value for the gyromagnetic constant in 2006 (CODATA 2006). This value is γp′=2.675153362 ⋅ 108 T-1 s-11 (Rev. Mod. Phys. Vol 80, 2008). In order to comply with international standards IAGA also adopted this value, to replace a value first adopted in 1991. Observatories and instrument manufacturers should be aware of this change and, if necessary, implement the 2006 CODATA value if they have not already done so. The difference between the 1991 and 2006 constants, however, amounts to only 15pT in 50,000nT and thus is within the noise level of most present day observatories reporting 1-minute data to INTERMAGNET standards. Therefore the 2006 value can be safely adopted without problem, even though simultaneous implementation by all observatories was not guaranteed.

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