Owner`s manual

Commentary on Species Adjustment
In 1992, a study was conducted at the Forest Research Laboratory
of Oregon State University on species correction for the Wagner
Hand-Held Moisture Meters. The species tested were Douglas Fir,
Lodgepole Pine, Western Red Cedar, Western Hemlock, White Fir,
Western Larch, Engelmann Spruce, and White Oak. Three to four
40-piece samples of each species were tested. Specific gravity was
found to be the primary factor on species adjustment. A species
equation as a function of specific gravity and the meter reading was
obtained using multiple-regression technique
(R-square = 0.95) as follows:
AF = 8.77 + (0.25 * MM) - (15.86 * SG) - (0.62 * SG * MM)
in which
AF = Adjustment Factor
MM = Meter Reading
SG = Species average Specific Gravity in oven dry weight and 12%
moisture-content volume basis.
The species adjustments provide the adjusted moisture
measurements that are based on the species adjustment determined
using the species adjustment equation, with rounding to the nearest
0.5.
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.
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 your Wagner Hand-Held Moisture Meter 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.
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