I have not have these very long however have tested them a couple of times. I placed these two meters along with a different model tester I had previously purchased.. I put them in the planter as close as possible without touching each other with the same depth in the soil. The readings on all three were fairly similar. I tried all three in another pot where I have a small Emerald Cedar tree and again all three readings were very similar. Make sure to clean off the rods after every use. So far, so good!