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.

dV = dMC rho

where
dV is the change in volume (within ±20% for most woods)
dMC is the change in moisture content
rho is the specific gravity (density) of the wood.

So, in adapting from 70% RH outdoors to 20% indoors, MC changes 10%, from 15% to 5%, and a wood of density 0.45 shrinks about 10% of 0.45, 4.5% in volume. The change in dimension tangentially will be about 64% of the volume change - 2.9%, the radial change 36% of the volume change - 1.6% (again, ±20% for most woods).

What is the moisture content (MC) of wood compared to its dry weight? Typically 60% for green hardwoods, up to double that for softwoods. The moisture is in two forms - chemically bound and free. The first aim of seasoning lumber is to degrade the chemical bonds to water, so that all that remains is free to move. This happens faster at higher temperatures, which is why kiln drying saves so much time. However, too-high kiln temperatures degrade wood, and most kiln drying is done as quickly as possible to produce cheap construction grade softwood. That’s why kiln drying has a bad name among instrument makers.

Skilled kiln drying can actually produce better wood than air drying. When wood is air dried, the outside dries faster than the inside, and this results in residual stresses in the wood. If the kiln humidity is controlled to match that of the wood throughout the process, and the high temperature is used just to speed up the rate at which the chemical bonds are degraded and moisture equilibrium is reached, residual stresses can be significantly reduced below those of air dried wood. But, there is no way to know, just looking at a piece of wood.

* Regularly clean and maintain gutters, and ensure that they drain away from the foundation of the building structure.
* Install and run exhaust fans in the bathroom and kitchen or open windows for adequate ventilation.
* Vent all fans and appliances to the outside of the home.
* Do not arrange or store items (furniture, storage boxes, etc.) so that they touch the interior side of exterior walls.
* Dry all clothes in a dryer that vents to the outside or use a clothesline outside.
* Cover dirt floors in basements and/or crawlspaces with plastic or other type of vapor barrier.
* Repair all plumbing leaks, roof leaks or problems, and cracks in foundation walls as soon as possible.
* Ensure that soil and landscaping near the structure’s foundation are graded away from the structure.
* Install floor drains or sump pumps in basements as necessary.
* Keep the temperature inside the home comfortable—not excessively hot in the winter or cool in the summer. Drastic changes between indoor and outdoor temperatures can contribute greatly to moisture problems.

Further precautionary steps can be taken to control moisture in the home environment during initial construction or any subsequent renovations. The New England Asthma Regional Council has developed excellent guidelines for building healthy homes and also offers links to numerous other healthy homes building resources.

* Rusting metal
* Condensation on piping and/or windows
* Rotting wood
* Mold growth
* Peeling paint, wallpaper, or other blistering materials
* Deterioration of other structural items
* Visible water leaks and/or stains
* Discoloration of various surfaces
* Musty odors
* Standing water

The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second.

Note that the effect of this definition is to fix the speed of light in vacuum at exactly 299 792 458 m·s-1. The original international prototype of the meter, which was sanctioned by the 1st CGPM in 1889, is still kept at the BIPM under the conditions specified in 1889.