Geomagnetic Observatory

Geomagnetic plots live data from the world's magnetic observatories on Apple devices. Pick a station and monitor Earth's magnetic field: both its total intensity and vector components. It downloads only the slice of data you are looking at, and only the minutes it doesn't already have, so it stays quick and keeps working offline once data is cached. It is free and open source, and draws on the INTERMAGNET network of observatories.