This includes infrasonic and hydrophone measurements. Not applicable Should be zero. Usually for power supply voltages, or line voltages. Instrument Code E Orientation code Designate as desired, make mnemonic as possible, use numbers for test points, etc. They measure the part of the field vector which is aligned with the measurement coil.
Many magnetometers are three axis.
The instrument will typically be oriented to local magnetic north. The dip and azimuth should describe this in terms of the geographic north. Some magnetometers do not record any vector quantity associated with the signal, but record the total intensity. Temperature recordings may also be essential for meaningful results. All other letters available for mnemonic source types.