If this app, "Compass Resolution" is used when a strong tornado is passing by, the geomagnetic field variations are supposed to be appeared as mentioned in the description of iPad app "GeoField".
Once user starts the app the user can recognize the small variations of geomagnetic field ( < 0.5 micro Tesla) on screen. The variations of horizontal and vertical components are monitored from start time.
Innermost circle (white) is corresponded to the z-component value (vertical component) at start time; the variation of z-component value is plotted outside the circle if the variation is positive and inside the circle if the variation is negative.
The second circle (black) is corresponded to the horizontal intensity at start time; the horizontal intensity variation is plotted outside and inside the circle as in the plotting of z-component.
The green needles inside the innermost circle represent directional changes of horizontal B-field and it's directional fluctuations.
To see the small variations, a circular magnifying glass is included that is popped out if one finger is touched inside the compass. Also, small angular deviations in horizontal components are displayed on left upper screen.
As the default settings "Low Pass Filter" is set to 0.05, "Average Number" is set to 5, and "Display Limit" is set to 2 degrees; however, user can change these settings and test the sensitivity and resolution of compass.
To visualize small variations the scales can be adjusted using Slider, and last 120 data points are traced.
The level of device is automatically adjusted to the flat level as if the device is being laid on a flat surface.
The settings, "Average Number" and "Low Pass Filter" affect on app performance and sensitivity. To get a high resolution the sensitivity of compass need to be negotiated. Anyhow, after user start/restart the app it will be restarted automatically after displaying first 120 data points.