I googled 'soil ph npk test meter' and found the one in the link below for $42 (but no photo).

So they do exist. I've never heard of them before, so I don't know how well they work. For the price, and if it really does work, it seems like a good deal. Keep a good grip on the receipt.

If you have a separate source of N, P & K, you might try testing them separately. In the link below, the description says "The 4-in-1 Electronic Meter ( picture not shown) features 3 probes that allow you to measure soil pH, soil moisture, light intensity, and total combined N-P-K (soil fertility)". TOTAL COMBINED NPK? Does that mean that if the K reads 20, and there's no N & P, that it still indicates that all is well???

As cynical and suspicious as I am, I would get the brand and the website, and contact them for some specifics.

Sue

Here is a link that might be useful: 4-in-1 electronic soil meter

I aloso do have one of those HD/FM testers.I also do not believe in its accuracy
in testing N,,P,,K. But I can live with its PH measurement.
Having started my garden from a virgin Georgis red clay, and grown
for 3 years in it, I can almost feel its heart beats by now an the ph gage is for double checing.
With native acid soil, as we have here, there is no quick fix. You have to do it over years, little by little. So the gadget comes handy sometimes.

We have an extension coop with the university of florida (an Ag center as it is called) and they test the soil for a small fee if you bring it to them. Check on that if your only gonna check it once a year.

Here is a link that might be useful: university of florida ag center

I have one and I love it. I consider it an estimate, not "gospel' but if the lows are looking too low, or the highs too high I adjust it and so far so good. I find as long as things are in the "ideal" range it's all good. I think it is not bad. The little Styrofoam looking sponge thingy that is in the box, it looks like junk, but keep it, you are suppose to clean the metal parts with it.