Albert,

It sounds like you are describing a "soil moisture meter" alright. Some also have a switch to read soil pH & ambient light, and they don't even require batteries. For soil measurements, they use dissimilar metals in the probes and measure the electrical potential between them - very small levels of voltage/current.

While you could experiment depending on the lowest range of your meter, you probably have to do a large sampling of measurements and create some sort of reference chart to interpret the results.

Considering you can buy these soil moisture meters from home-improvement stores in the garden department, for $5-10, I'd be more inclined to buy one!