Gardening

So heres the thing with these devices, they aren't accurate but they are sort of precise.

Every soil is different, but the same soil at roughly the same wetness will fairly precisely read the same way each time.

So in conjunction with a much more accurate readout from lab equipment, you can get an initial handful of readings from your specific patch of land and record what this meter read, so you benchmark the actual spot you wanna hit with the dial for your very specific fertilizer comp you use. Say, mark it with a little marker.

Then for the rest of that season, this little meter should be pretty solid enough because you first took the time to calibrate it against more accurate tools

At which point its not a reader on its own, its merely a well calibrated gauge, calibrated against other tooling.

And that will work fairly well enough for most use cases. The point of the device isn't to track precisely getting your mixes right, the point is it will instantly point out if something has gone very wrong before it gets worse.