> ## Documentation Index > Fetch the complete documentation index at: https://data.avert.ldeo.columbia.edu/llms.txt > Use this file to discover all available pages before exploring further. # Instruments > Magnetic field data We are using Mag-13 three-axis fluxgate magnetometers manufactured by Bartington Instruments. For more information, please see the [Bartington Instruments webpage](https://www.bartington.com/products/high-performance-magnetometers/mag-13-three-axis/). The voltage signals output by the sensing coils in this instrument are digitised using the 24-bit Nanometrics Centaur datalogger, which we also use to digitise the signals from our analogue seismometers. A top-down picture of one of our fluxgate magnetometers in the ground at Okmok volcano, in the Aleutians. This device, approximately 25 cm in length, contains 3 orthogonal fluxgate magnetometers that continuously measure the orientation and magnitude of the local magnetic field.

A top-down picture of one of our fluxgate magnetometers in the ground at Okmok volcano, in the Aleutians. This device, approximately 25 cm in length, contains 3 orthogonal fluxgate magnetometers that continuously measure the orientation and magnitude of the local magnetic field.

## Example data plots Some sample data from the AV.OKBR magnetometer, deployed inside the Okmok caldera, are shown below. An example snapshot of the vertical component of the magnetic field, recorded at the station OKBR, on Okmok. The data show variations on a period of approximately a day, as well as short-term variations likely related to changes in activity in the ionosphere/magnetosphere and, hopefully, the signals we are interested in!

An example snapshot of the vertical component of the magnetic field, recorded at the station OKBR, on Okmok. The data show variations on a period of approximately a day, as well as short-term variations likely related to changes in activity in the ionosphere/magnetosphere and, hopefully, the signals we are interested in!