Two measurements determine the scaling cylinder of a log segment scaling diameter and scaling length. The scaling cylinder is an imaginary cylinder extending the scaling length of a log segment with identical diameters on both ends.


The large end diameter of the cylinder is the same as
the scaling diameter on the small end. Gross scale of a log is based on the
total board foot contents within this imaginary cylinder. 

The Coconino Scribner decimal C log rule measures diameters on the onehalfinch rather than the fullinch. For example, using a standard tape measure, a scaling diameter of 10 would be any diameter that measures between 9 ½ to just under 10 ½. The minimum top diameter normally considered in scaling is 6 (5.51 actual inches). When the narrowway is less than 6 (5.51 actual inches), the log will be scaled back to the next shorter log length that meets the minimum top diameter requirement (this shorter log length is reflected in twofoot multiples with full trim). Log segmenting will then be done using this new or cutback length.
When making diameter measurements, always remember the following:
· Diameters are measured on the smallest point on the log.
· Measurements are taken inside the bark.
· Measure through the true center of the log.
· Disregard all abnormal bumps and depressions (such as knot clusters, swells, or broken ends).
Diameter measurements are taken by finding the narrowest way first. If all logs were small and round, one
measurement would probably be all that was needed. However, trees grow in a variety of shapes.
When logs are delivered that are odd or oblong in shape, a second diameter
measurement is needed. The second measurement is taken at a rightangle (90 degrees) to the first (narrowest)
measurement. If one diameter measurement falls exactly on the halfinch, raise
it to the next higher fullinch. If both
measurements fall exactly on the halfinch, raise one and lower the other. The two measurements are then added together
and divided by two. If the final calculation ends in onehalf, the
onehalf is dropped. As an example: a
log with a diameter measurement of 12 the
narrowway and 15 at a right angle, has a scaling diameter of 13.

Acceptable log lengths are generally in twofoot multiples, plus 6 for trim allowance per segment. The maximum scaling length for a single segment log is 20 plus trim. When logs exceed 20 they are scaled as two or more segments, with the length of each segment being as close to the same as possible. On a buttcut, measure from the shortest side on the small end to the point where the scaling cylinder emerges on the butt. Second cut logs are measured from short side to short side.
To improve productivity, handling, and storage
capabilities, logs are frequently manufactured in lengths longer than 20
6. Since log segments are scaled with a
maximum scaling length of 20, it becomes necessary to obtain a smallend
scaling diameter for any other segment(s) within the log.
Determining Midpoint Diameter on Secondcut Logs 
Measure the small end diameter and the large end diameter; add both measurements together and divide by two. If the final calculation ends in onehalf (1/2), raise it to the next higher whole number. 
This log has small end diameter of 13 and a large end diameter of 18. 13 + 18 = 31 divided by 2 = 15 ½; raising the final ½ to the next higher whole number = 16 midpoint diameter. 
To determine
the rate of taper in butt logs, extensive studies were conducted on logs from
different areas. Results of these
studies were used to develop standard
taper rules for butt logs. Because of distinct differences in the rate
of taper from various areas, different taper rules will apply to various
regions.
Midpoint Taper
Determination for Multisegment Butt Logs 

1. NORTH IDAHO AREA (north of the Salmon River, and including the northeastern Washington area bounded by the Snake River on the south, to the Columbia River, north to the Okanogan River, north to Canada)  midpoint taper shall be a standard taper as follows: 

Larch & Lodgepole Pine Larch & Lodgepole Pine Cedar All Other Species All Species (except Larch & Lodgepole Pine) All Species 
21 48 49 60 21 40 21 40 41 60 61 and longer 
Shall be 1inch per segment. Shall be 2inch top segment, 1inch remaining segment. Shall be 2inches per segment. Allow 1inch taper on pieces with an odd top diameter; allow 2inch taper on pieces with an even top diameter (OddEven Rule). Take two measurements, small end and 16 up from the butt. The diameter at the 16 measurement point shall be determined by actual measure. Apply calculated taper distribution to determine scaling diameter of the second segment. Take two measurements, small end and top of the second segment up from the butt. The top diameter of the second segment shall be determined by actual measure. Apply calculated taper distribution to top segment(s) and standard taper rule for the appropriate species to bottom segment. 
2. SOUTHWEST 

Larch All Other Species 
21 40 21 40 
Shall be 1inch taper. Shall be 2inch taper. 
Multiplesegment butt logs not addressed shall be determined with actual taper applied. 

3. SOUTHEAST
a. TARGHEE NATIONAL FOREST AREA midpoint taper shall be a standard taper as follows: 

Douglas Fir, Alpine Fir, & Engelmann Spruce Lodgepole Pine Lodgepole Pine 
21 40 21 31 32 40 
Shall be 2inch taper. shall be 1inch taper. shall be 2inch taper. 
b. OTHER SOUTHEAST AREASmidpoint taper(s) shall be determined with actual taper applied. 

c. Multiplesegment butt logs not addressed shall be determined with actual taper applied. 

4. Except as previously addressed, the
buttlog taper tables developed by the USFS at the point of origin of the
forest products shall be utilized on all forest products scaled within the
state of 
There are four types of defect deduction methods
used in scaling logs. These methods are
used to arrive at the net scale
volume of a log by applying a given set of rules and procedures.
(1) Length cut is used to reduce the gross scaling length to a usable net scaling length. This method is used for larger interior rots (such as butt rots or conk rots) and also for undertrim or overtrim log lengths. 
This log has a 16 scaling diameter and a 16 scaling length, giving a gross volume of 16. The log has butt rot which is estimated to extend 4up the log. A log with a 12 scaling length and a 16 diameter would have a gross volume of 12, this would be the net volume for this log. 16 (gross volume)  12 (net volume) = 4 (defect) 
(2) Diameter cut is used to reduce the original gross scaling diameter to a smaller net scaling diameter. This method is used for defects such as sap rots and surface checks. 
This log has a scaling diameter of 20 and a scaling length of 16; the gross volume would be 28. The log has a collar of sap rot (oneinch thick) extending all the way around, leaving a firm 18 core. The gross scale of a 16 log with an 18 diameter would be 21; this would be the net scale for this log. 28 (gross volume) 21 (net volume) = 7 (defect) 
(3) Pie cut is used to reduce the gross scale for a portion that is missing or not merchantable. This method can be used for defects such as lightning scars or catfaces that do not affect the entire scaling cylinder. 

This log has a scaling diameter of 20, and a scaling length of 16 with a lightning scar that is estimated to affect Ό of the scaling cylinder. The gross scale of the log would be 28, divide this by 4 (one quarter of the cylinder) to determine the defect deduction. 28 (gross volume) = 7 (defect) 4 
(4) Squared defect cut is used to make deductions in the form of squares or rectangles from the interior of a scaling cylinder. This mathematical method is used for pitch seams, heart checks, and smaller interior rots. The formula for this is: Width (inches) x Height (inches) x Length (feet) = Defect volume in board feet (round this to the 15 nearest ten and drop the final zero) Numerous rules apply when using squared defect: ·
one inch is
added to allow for waste on both width and height dimensions ·
logs 15 and
shorter  measurements are taken from the large end of the
defect ·
logs 16
through 20  measurements are taken from the large and small
ends of the defect, then averaged to get the midpoint dimensions for the
width and height ·
if the squared defect
equals or exceeds the gross volume of a segment, the scaler must use a
different method of deduction. 
This log has a pitch seam that measures 1 x 11 on the small end and 2 x 14 on the large end. Since the log is shorter than 16, the largest end of the defect is used and one inch for waste is added to both the height and width measurements. 15 (height) x 3 (width) = 45 x 14 (length) = 630 = 42 rounded to the nearest zero = 4 (defect) 15 
This log has a heart rot that measures 14 on the small end, and 16 on
the large end. Since this log is 16 or longer in length, the two
measurements are averaged to obtain a midpoint diameter of the rot. One inch is
then added for waste to the averaged midpoint diameter. 14 +
16 = 30 =
15 (avg. midpoint) + 1
(waste) = 16
2 16 (height) x 16 (width) x 16 (length) = 273 rounded to the nearest zero = 27
(defect) 15 
Since lumber is usually sold in twofoot multiples, the net scale of a log is also determined in twofoot multiples. Any defects that would result in lumber length recovery shorter than six feet are treated as if they affect the entire length. Each log segment is always scaled on its own individual merits.

This diagram shows a
twosegment log with a scaling length of 32.
The top segment has a scaling diameter of 9 and a scaling length of 16
for a gross volume of 4. The butt
segment has a scaling diameter of 10 and a scaling length of 16 for a gross
volume of 6. There is no defect in
the top segment. The butt segment has
crook defect affecting ½ of 7 the remaining unaffected portion of the butt
segment is 9. To reflect lumber
length recovery in twofoot multiples, the crook defect is treated as if it
extended for 8. The defect deduction
is determined by the fraction of the length affected, converted to an
equivalent length cut in this example, ½ of 8, or a 4foot length
cut. The defect volume deduction for a
length cut is always the difference between the gross length volume and the
net length volume. 

16 (gross length) 12 (net length) = 4 (defect length) 
6 (gross
volume) 3 (net volume) = 3 (defect volume) 

Top segment +
Butt segment = Total Scale Volume 
Gross 4 + 6 = 10 
Defect 0 + 3 = 3 
Net 4 + 3 = 7 
