Very interesting experiment by Lori Gardi aka Fractal Woman regarding measuring the lines (or circles) of equal magnetic field strength, and termed isopotential or equal-potential lines. The isopotential lines appear to mirror the shapes formed by a ferrocell when a magnet or magnetic field is interacting with it. Very interesting stuff!
Experiment: Measuring Magnetic Isopotential Lines: https://youtu.be/Jwr0eZy7Hk8
More Hall Sensor Experiments: https://youtu.be/9l4AwOPHG0M