The specific systematic error due to rotation of the proton precession
magnetometer is analysed, the resulting error being within +/-OMEGA/g
amma, the ratio between the platform rotation rate and the proton gyro
magnetic constant. The commonly observed shift in sounding rocket-born
e proton magnetometer measurements, corresponding closely to twice the
rocket spin rate at re-entry into the denser atmosphere, is explained
. Optically pumped magnetometers with a much larger gyromagnetic const
ant are correspondingly less affected by this error.