1.Pitch.
2.Needleless rice.
Pin hygrometers use two (or more) electrodes to penetrate wood material to read the %MC of that material using the principle of electrical resistance. In a two-pin meter, with one pin emitting current and the other pin receiving it, the meter interprets the impedance of the current to the current. Since wood is an insulator and water is a conductor, the less resistance to current flow, the higher the moisture content of the wood.
Pinless meters, on the other hand, use electromagnetic radio waves to scan the meter to scan wood samples beneath the plate. These meters are sometimes called non-invasive hygrometers because they don't have to physically penetrate the wood surface to get a reading.
