  The precision of the values of a magnetic field generated by electromagnetic
flux compression was investigated in ultra-high magnetic fields of up to 700 T.
In an attempt to calibrate the magnetic field measured by pickup coils, precise
Faraday rotation (FR) measurements were conducted on optical (quartz and crown)
glasses. A discernible "turn-around" phenomenon was observed in the FR signal
as well as the pickup coils before the end of a liner implosion. We found that
the magnetic field measured by pickup coils should be corrected by taking into
account the high-frequency response of the signal transmission line. Near the
peak magnetic field, however, the pickup coils failed to provide reliable
values, leaving the FR measurement as the only method to precisely measure an
extremely high magnetic fields.
