  The solar mean magnetic field (SMMF) provided by the Wilcox Solar Observatory
(WSO) is compared with the SMMF acquired by the \textit{Helioseismic and
Magnetic Imager} (HMI) onboard the \textit{Solar Dynamic Observatory} (SDO). We
found that despite the different spectral lines and measurement techniques used
in both instruments the Pearson correlation coefficient between these two
datasets equals 0.86 while the conversion factor is very close to unity: B(HMI)
= 0.99(2)B(WSO). We also discuss artifacts of the SDO/HMI magnetic field
measurements, namely the 12 and 24-hour oscillations in SMMF and in sunspots
magnetic fields that might be caused by orbital motions of the spacecraft. The
artificial harmonics of SMMF reveal significant changes in amplitude and the
nearly stable phase. The connection between the 24-hour harmonic amplitude of
SMMF and the presence of sunspots is examined. We also found that opposite
phase artificial 12 and/or 24-hour oscillations exist in sunspots of opposite
polarities.
