Don’t rely on measurements by electrical methods to better than ±2% absolute moisture content, no matter what a manufacturer claims. (C.Skaar, “Wood-Water Relations”, 1988, discusses many variances which affect such resistance measurements.) Volt-amp-ohmmeters are carried by many electronics stores, but almost none have a resistance range high enough to measure the MC of any but the wettest wood.

Wood takes longer to come to equilibrium at its center than on its surface, so for thick beams the surface moisture measurements of the pin meters are less accurate. They are less accurate for wood that is less than 20 mm thick. It’s not easy to push pins into hardwoods. And, the wood is damaged by the measurement.

A better method for the wood used by instrument makers should be to make two flat electrodes, press them to the surface of the wood, one each side, with a woodworkers clamp, and measure the resistance between them. Unfortunately, it doesn’t work, because a flat plate can’t make adequate contact with the wood fibers unless pressed on so firmly (>10 kg/cm²) that the wood is crushed. Various conductive pastes are available, such as the kind doctors use for electrocardiograms, but I have yet to find one that doesn’t hopelessly stain wood.

However, what is most important for woodworkers is whether or not the wood has reached equilibrium in the workshop. Successive thickness measurements of the same piece of wood can tell you that directly, without any electric gadgets. You will need a dial caliper that will measure to a few tenths of a percent. Then, mark the exact place where your measurements are being taken, and don’t lose your piece of paper you write the numbers on!

Of course, if you want to check any of this, cut a piece off your wood, weigh it, then dry it in an oven until it stops decreasing in weight. Then you will know precisely how much moisture there was in your sample. That’s how scientists do it.