Accurate
Technology
Pro-60
Page
8
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12
Wood is not a uniform material. Specific gravity of solid-sawn lumber varies within the
piece and among pieces. In the OSU study, the average specific gravity for each
species differed from the individual sample by plus or minus 1% to plus or minus 8%.
For general applications, average specific gravity values can be found in the Wood
Handbook (USDA Agriculture Handbook No. 72, 1999). Except for one species for
which the experimental value is 7% higher, the species’ overall average specific gravity
values obtained in the OSU study are comparable with those in the Wood Handbook.
The exception may be caused by unknown biases in the sampling scheme. The Wood
Handbook values are used in the tables, except for the imported species, unless
otherwise noted.
Species adjustment can be determined for lumber sorted, or otherwise known, to have
specific gravity different from the species’ average. One example is lumber graded
under the Dense rules. If the specific gravity of a lumber sample is known, species
adjustment can be determined by the species adjustment equation.
The species adjustment equation provides a way to expand the use of the Pro-60
Hand-Held Moisture Meters for lumber of any species groups having similar species-
specific gravity values. One example is Hem-Fir. For a species group, one way to
determine the species adjustment is by the use of a weighted average of the individual
species’ average specific gravity values. The weighing procedure used in the ASTM
D2555 by standing timber volume can be used. Species adjustment is not
recommended for any species group having a broad range of species-specific gravity
values. There are no recognized limits on species group species adjustment. Species
adjustment for species groups should be used with knowledge on the variability on
species involved and the affect of it on species adjustment. If the species mix in the
lumber production of a species group is controlled or known to have specific gravity
different from that used for the species group, a better estimation of species
adjustment can be determined using the known specific gravity in the above species
correction equation.
DETERMINING SPECIFIC GRAVITY
Determining the Adjustment Factor for an Unknown Species
The Specific Gravity Chart is based on specific gravity of solid wood is provided on a
separate sheet included with the meter. If you don’t know the species of the wood you
are using, or the specific gravity differs from the handbook because of a different
growing region, use the following procedure.
