Types of wood structural defects 
test method 
graphical 
Calculation method 
Twist pattern 
The inclined height from the starting point to the end point of the twist pattern (shown as chord length in the cross section of the small head) or the ratio of the arc length to the diameter or circumference length of the inspection ruler shall be measured within the small head or any 1m range or within the range of any material length excluding the large head 1m, expressed as a percentage 

The calculation is based on formula (1)
z₁ = h / D × 100%
The calculation is based on formula (2)
z₂ = a / π D * 100%
Where:
Z ₁, Z2: torsion degree (%)
h: Tilt height of twist pattern (CM)
a: Inclined arc length of twist pattern (CM)
D: Gauge diameter (CM)
π D: Circumference (CM)

Stress wood 
Generally, there are no restrictions. The width, length or area of the defect can be measured by special materials or advanced materials, and compared with the corresponding size or area of the cross section, it is calculated by percentage; Or measure the linear distance between the geometric center of the crosssection and the medullary core, and compare it with the long diameter or average diameter or ruler diameter of the crosssection, calculated as a percentage 

R = L / D × 100%
Where:
R: Eccentricity or eccentricity of stress wood
50: Linear distance between geometric center of log section and pith Center (CM)
D: Gauge diameter (CM)

Double or multi heart wood 
It is not detected, but its existence should be noted 
Eccentric timber 
The maximum offset between the ellipse center and the geometric center of log end face shall be detected, expressed as the percentage of maximum offset or maximum offset to corresponding end face diameter 
Withered 
The radial depth is measured by percentage compared with the diameter of the ruler; Or check the width and length of the withered, and compare with the corresponding size, in percentage 

The formula for calculating the ratio of withered depth is as follows:
s = h / D × 100%
Where:
s: Dry depth ratio
h: Radial depth of withering (CM)
D: Gauge diameter (CM)

Sandwich leather 
The maximum thickness A1 of the inner sheath should be detected, expressed by the ratio of the maximum thickness or the maximum thickness to the diameter D of the inspection ruler 

Z ₁ = a ₁ or Z ₁ = a ₁ / D
Where:
Z ₁: the maximum thickness of the inner sheath or the ratio between the maximum thickness and the diameter of the inspection ruler
A: maximum thickness of inner skin (CM)
D: Gauge diameter (CM)

The length, width and depth of the outer sheath shall be tested. It is expressed by the ratio of width, depth to the diameter of the ruler or the ratio of length to length 

The formula (1) is used to calculate the outer sheath: Z Ψ = a Ψ / d
The formula (2): Z ₃ = h Ψ / D
The formula (3) is used to calculate the outer sheath: Z Ψ = l Ψ / L
Where:
Z Ψ: ratio of skin width to gauge diameter (%)
Z ₃: ratio of skin depth to gauge diameter (%)
Z ₄: ratio of skin length to gauge diameter (%)
A Ψ: width of outer skin (CM)
H Ψ: the depth of the outer skin (CM)
L Ψ: length of outer skin (CM)
D: Gauge diameter (CM)
50: Gauge length (CM)

Dendroma 
If the appearance is intact, there is no restriction generally, but if there is a cavity or causes internal decay of the trunk, it is calculated as dead node or leaky node 
Pseudo heartwood 
The diameter mouth of the circumscribed circle of the pseudo heartwood should be detected and expressed by the diameter or the percentage between the diameter and the diameter D of the end face 


Sapwood inside 
The width of the ring part containing sapwood growth ring (growth ring) is measured and expressed by the width or the percentage of the width and the diameter of the ruler (dimension D, a) 

