For those who wish to build their own magnetic storm detector, there are two popular designs--the variometer and the fluxgate --which are sensitive enough to detect storm-induced changes in the Earth's magnetic field, and technologically within reach of the amateur observer.
The variometer is the oldest and simplest instrument for monitoring the Earth's magnetic field.
The simplicity and low cost of the basic variometer are advantages but the lack of automatic recording of the output is its disadvantage.
In contrast to the variometer, the fluxgate is a much more complex, and recent (developed in the 1930s), sensor.
For this paper, a fluxgate sensor and a home-made variometer were installed in the author's study.
To log the outputs from the sensors a home-made data acquisition system was constructed which could count the pulses from the fluxgate and digitise the analogue signal from the variometer.
The variometer was constructed in a cylindrical plastic food storage jar, 12cm in diameter and 18cm high.