In 2012 I was temporarily housebound. I used the time to explore an interest I had in geophysics, specifically resistivity surveying.
I read a paper by Bruce Bevan which included a figure showing how simple the principle of resistivity is and how it can be carried out using nothing more than four nails, a battery and a multi-meter.
I was intrigued so I set out to make my own. My first attempt at building a meter saw me wire the four nails to two multi-meters and a switch (allowing me to turn the battery on-and-off).
The results were plotted using a simple grey scale in Python. For such a basic setup I think the output is remarkable. The main issue going forward is speed. It is very slow!