Reading and my experience both tell me that below 20% is good, 15% is even better. Most wood dries to 20 - 25% fairly quickly (< 1 yr) as the water between and inside the wood cells is eliminated. The remaining water is "bound" within the cell walls themselves (a constituent of the wall) and is much slower to exit.
I've got one of those HF meters. I doubt they are well calibrated so I did a control test first thing using a fresh split for a baseline and sanity check. This device is also not exactly heavy duty so I use it as follows to maximize life expectancy.
Re-split a piece of wood to expose its middle for testing.
Work on a stable surface to prevent fumbling while tines are embedded in split.
Lightly press the tines in to create two little pilot holes at a 90* angle to split.
Push an ice pick into both pilot holes creating more depth and increasing tine contact surface.
Hold the whole thing very carefully (one fumble and that delicate sucker will be toast).
Press the 'High' button, get reading, press the 'Low' button.
Mo's Proposed Warning Label:
Do not poke tines into skin, eyes, or genitals.
Do not use hammer to set tines.
Do not use without battery.
