Four pin will give more comparable results.
Two pin is much more dependant on probe condition, and contact with the
wood, four pin - ideally - should not depend on this.
A sharp plug cutter, an oven at 100C for an hour, and a sensitive scale
is of course the best way.
The basic theory of the two wire probes is similar to measuring the
springyness of a spring, with two springy probes.
It's hard to measure the springyness (resistance) of the spring,
seperately from the probes, which tend to vary a great deal.
If with the four wire probes, you apply a constant tension with one set,
and then measure with the other, you can get an accurate figure.
The body fat scales use a similar sort of idea - though they are
designed to accurately -sort-of- measure the resistance of the thighs.
True enough for planks. With the TDT (Turn, Dry,Turn) process, a moisture
meter is absolutely unnecessary. The meter relies on continuous long grain,
something not found in many places on a standard bowl form. The base or
"foot" is the only place I can think of.
Better to stack such things to dry, pull when you think they should be, and
then weigh them. If they weigh basically the same after a week, they're
ready to turn. It's equilibrium, not absolute numbers that count.
Absolutes aren't even that important in flat work except as trend
indications. If the hygrometer says the wood should be at equilibrium at
12%, and the meter shows 18, you need to wait. Of course you still follow
good practice in construction, building loose with dry wood, tight with wet
to accommodate seasonal changes. For me, in a heated home, that means 14%
in summer and 6% or less in winter.
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