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An ideal MC must be fixed to
enable calculation of variations in dimension. However, a
normal MC value is not an absolute value, because there are
differences in the MC of boards that have been dried at the
same time. Melrose boards are characterized by a MC between
6% and 9%. Variations have different causes, for example,
the variation in size of the raw lumber, differing humidity
rates in trees before they are cut and dried, etc.
If the rate is based on an average, the result, according
to the Wood Humidity Content Table, is a relative humidity
rate of 37.5% for a MC of 7.3%. However, we have chosen
a slightly different method of calculation which consists
of considering the wood as stable in a relative humidity
environment varying between 35% and 40%. In this case the
MC obtained ranges from 6.9% to 7.7%.
This ruler shows fractions and offers their equivalence
in millimetres.
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