It’s not a great solution, it’s prone to false readings but its approximate enough for the home gardener.

I have a small handful of plants. It’s good enough for me. I completely agree that if it were my livelihood I would be sending it off to a lab. If something happens to my garden I get less salsa and have to buy tomatoes at the store. If something happens to a farm they’re fucked for the year unless they get on top of it.