For the distilled water test, a ball jar (the ones used for canning) is a good size. But whatever container you use, make sure it doesn’t have any residue in it. Fill it up with enough distilled water to cover the entire silver part of the POGO (basically the water line should go up the shaft a few inches or so past the integrated sensor). Also there should be about an inch or so of water on all sides of the sensor. Take a reading and record the app measurements. It is a rough test but will tell us a lot about the precision of the sensor. Note that if the sensor is worn, that will impact this test.
If tested properly in distilled water, you should get something in the 70's for moisture and between 0.00 and 0.02 EC (0.0 to 0.02 dS/m.)