A tree-trunk-diameter gauge has an adjustment which enables, by a simple multiplication factor of the scale indication, the use of the gauge for a range of larger diameter trees in addition to a range of smaller diameter trees. The gauge can be mounted by holes in the gauge body and an elastic band or by a hook and loop fastener to the back of the hand of the user.

FIELD OF THE INVENTION 
Our present invention relates to a tree-trunk-diameter gauge and, more 
particularly, to a gauge for measuring the diameters of tree trunks and 
which can be held on the back of the hand of a user and is suitable for 
determining the diameters of a wide range of tree trunks. 
BACKGROUND OF THE INVENTION 
Gauges for determining the diameter of a tree trunk are described, for 
example, in Austrian patent 172,607 and German patent 908,416, both from 
1952 and which are in the form of angles which can be held against a tree 
trunk and can indicate directly the trunk diameter utilizing an indicating 
pin which is sited across the scale toward a side of the tree trunk. This 
device has the advantage that it does not require complex mechanical 
manipulation of parts thereof to obtain a measurement and can be held by 
only one hand of the user. It has been found that the use of such a gauge 
enables even large diameter tree trunks to be measured where parallel-jaw 
calipers could not be used. However, for the measurement of larger trees, 
the gauge had to be originally fabricated to be twice as large. 
Furthermore, it is often desired with such gauges to establish a fixed 
distance of the indicator needle from the eyes of the user, i.e. to ensure 
reproducible measurements, and that could not be achieved with earlier 
devices of the type described. 
Finally it has been found that measurements should be taken on trees with a 
certain spatial orientation and that has also been difficult with 
conventional devices. 
OBJECTS OF THE INVENTION 
It is, therefore, the principal object of the present invention to provide 
a light-weight gauge which, while suitable for measurement of tree 
diameters up to say 100 cm can also be used to measure trunk diameters 
which can be significantly larger, say twice as large, without difficulty 
and while nevertheless retaining the hand of the user as free as possible 
for other purposes. 
Another object of this invention is to provide an improved tree diameter 
gauge which facilitates specific orientation of the gauge on the tree in 
space so that it is not necessary, for example, to first determine 
directions in space before a measurement is to be carried out. 
It is also an object of the invention to provide an improved device for 
angle count sampling which ensures high reproducibility of results by 
establishing a fixed distance of the user's eyes from the gauge. 
SUMMARY OF THE INVENTION 
These objects and others which will become apparent hereinafter are 
attained, in accordance with the invention, in a gauge which can be 
mounted on the back of one hand of a user in such manner that the fingers 
of the user remain free for operating a tree marking device, a calculator, 
or for any other purpose and wherein the gauge may be used for trees of 
diameters up to say 100 cm, i.e. trees of a lower diameter range, but 
wherein the device is readily adaptable by the releasable attachment of a 
fixture or further body thereto, for the measurement of a larger range of 
tree diameters. 
In practice, this can be accomplished by providing the angle body of the 
gauge with three holes, through two of which an elastic band can be passed 
to attach the gauge to the back of the hand of the user, the holes serving 
in addition for connection to the attachment to the basic gauge body. The 
underside of the gauge can, if desired, be provided with a recess in which 
a hook and loop fastener may be adhesively secured to serve as an 
attachment to the back of the hand of the user. The arcuate scale which is 
provided according to the invention can be provided with a band of a width 
which is so determined based upon the center-to-center spacing of the 
individual viewer's eyes, that each eye images the indicator pin or needle 
at a respective end of that band when the gauge is held at a fixed 
distance from the eyes of the user, say a distance from the eyes of the 
user to the indicator needle of three times the distance from the needle 
to the scale which is centered on the needle. 
Since the user can readily establish the eye distance by holding up the 
gauge and matching the images of the left and right eye with the right and 
left edges of the band, the gauge offers reproducibility. 
The orientation in space of the gauge can be established according to the 
invention by providing a magnetic compass, i.e. a compass whose magnetic 
needle indicates north and south directly on the body of the gauge. 
The tree-trunk-diameter gauge of the invention can thus comprise: 
a rigid angle body formed with a first shank and a second shank adjoining 
the first shank at a vertex of the body; 
an arm pivotably mounted on the second shank proximal to the vertex between 
a compact position wherein the arm lies along the second shank and a 
working position wherein the arm extends from the vertex, whereby the arm 
and the first shank engage spaced apart locations on a tree trunk; 
an arcuate scale on an inner side of the first shank convexly facing toward 
an end of the second shank remote from the vertex; 
means at the end cooperating with the scale and positionable in line with a 
side of the tree trunk for indicating on the scale a diameter of the tree 
trunk; and 
an attachment connectable with the body and dimensioned to contact tree 
trunks of larger trees while enabling the indicator means to indicate the 
diameters thereof on the scale upon application of a multiplication 
factor. 
Preferably the attachment comprises a further rigid angle body formed with 
a respective first shank and a respective second shank adjoining the first 
shank of the further body at a respective vertex thereof, and a further 
arm pivotably mounted on the second shank of the further body proximal to 
the vertex of the further body for swinging movement between a compact 
position wherein the further arm lies along the second shank of the 
further body and a working position wherein the further arm extends from 
the vertex of the further body, the further body having means for 
connecting the further body to the first shank of the first-mentioned 
body. 
Advantageously corresponding points on the further body are twice the 
distance from the indicator means than respective points of the 
first-mentioned body and the multiplication factor is two. 
A segment method of measuring diameter and which can utilize the compass on 
the gauge body has been described in Austrian patent 400,765.

SPECIFIC DESCRIPTION 
Basically the gauge of the present invention comprises a primary gauge 
member 10 in the form of a fixed angle having a first shank 11, a second 
shank 12 angularly adjoining the first shank, a means represented at 13, 
for example in FIG. 12, at the free end of the second shank 12 remote from 
the vertex 14 thereof for cooperating with an arcuate scale 15 along the 
inner side of the shank 11, and an arm 16 which is pivotable about a screw 
17 when a butterfly nut 18 is loosened to enable that arm to swing into 
its extended position as shown in FIG. 2 where the arm 16 extends along 
the shank 12. 
As can be seen in FIG. 2A, the underside of the fixed angle, preferably 
along the shank 11, may be provided with a recess 19 in which a layer of 
adhesive 20 can bond a hook and loop fastener 21 to enable attachment of 
the device, e.g. to a handle arrangement when a rubber band as described 
below is not used to support the gauge of FIGS. 1 and 2 on the back of the 
hand of a user. 
The scale 15 has been shown in FIG. 3 and comprises two scales one above 
the other, the upper scale representing the diameter of a tree in 
centimeters or inches. 
As can be seen from FIG. 1, the device 13 can be a viewing pin or needle 
which can be rotated into an upstanding position from a position in which 
it lies along the shank 12. 
The unit 10 can be three holes represented at 22, 23 and 24, for example, 
the holes 22 and 24 receiving an elastic band through which the hand can 
be inserted. The holes 22 and 23 can, as will be apparent, receive gauge 
attachment devices which hold a member 30 on the member 10 when the gauge 
is to be used for measuring the diameter of trees of twice the diameter 
for which the gauge 10 is designed. 
Further details of the gauge 10 can be seen in FIG. 4 in which the line of 
sight of the needle 13 cooperating with the scale 15 is shown as a line 
31. The rubber band 32 passing through the holes 22 and 24 is here also 
visible. In FIGS. 4 and 5, moreover, we have shown a compass 33 in the 
shank 11, enabling the arm 16 to be aligned with the north, south, east or 
west axes as desired. In FIG. 5, the arm 16 is parallel to the needle 34 
of the compass 33 directed to north. 
In the compact state of the gauge of FIG. 1, wherein the arm 16 is disposed 
along the shank 12, the dimensions of the gauge are about 
27.times.19.times.2 cm and its weight can be about 130 g. It is composed 
of shape-retentive and weather-resistant synthetic resin. The viewing 
needle 13 has been shown to be erect in FIGS. 1 and 2, although usually in 
the closed or compact state of the gauge, that needle will lie along the 
shank 12. In FIG. 1, knots of the rubber band 32 can be seen above the 
holes 22 and 24 to prevent the rubber band from being pulled out. 
The region in which the holes are located can be recessed both above and 
below the gauge each by one-third of the thickness thereof an can form the 
recess 20 previously described in which a hook and loop fastener is 
received. 
In FIG. 2, the rubber band can hold the gauge on the left hand of the user 
so that the gauge need not be held on a handle, but rather the hand can 
also grip the handle 25 of a scraper or marking tool 26. When a marking 
tool is not gripped by the user, the free fingers of the same hand that 
supports the gauge can be used to input data into an electronic 
calculator. For better attachment on the back of the hand, a strap of the 
hook and loop fastener passing around the hand can engage the portion 21 
of the hook and loop fastener shown in FIG. 2A. 
The projection of the viewing needle 13 upon the scale 15 can provide a 
reading on the upper scale of the trunk diameter of a tree between 4 and 
100 cm or 2 and 40 inches. The lower scale gives the number of trees per 
hectare (n/ha) or per acre using Relaskop.RTM. factor 4 m.sup.2 /ha (or 20 
sq. ft/acre) in a tree selection. 
When the attachment 30 is used for tree trunks of double diameter (FIG. 5), 
the reading on the upper scale is doubled while that on the lower scale is 
a quarter in the case of the Relaskop.RTM. selection. 
FIG. 9 clarifies the geometry and also the configuration of the attachment 
for doubled trunk diameter: the viewing needle is located at V, a centrum 
for central projections of the points a, b and c of the gauge 10 and the 
points A, B and C at twice the distance for the attachment. 
As can be seen from FIG. 9, practically all of the significant dimensions 
of the gauge are doubled and thus the diameter reading of the scale which 
is unchanged must be doubled. However, since the cross sectional area is 
multiplied by a factor of four with doubling of the diameter, the value to 
be read from the lower n/ha scale is only one-quarter with a counting 
factor of 4 m.sup.2 /ha (or 20 sqft/acre) or one-eighth with a counting 
factor of 2 m.sup.2 /ha (or 10 sq. ft/acre). The tree trunk considered in 
a given hectare must be provided in a sufficiently large number that their 
individual cross sections is treated in meters square in the counting 
factor. 
The attachment can be connected at the holes 2, 3 along the line a-b. 
As can be seen from FIG. 6, the attachment 30 can have a narrow portion 35 
bordered by an opening 36 to serve as a handle when the holes 22 and 23 
serve to connect the attachment 30 to the gauge 10. More specifically the 
attachment 10 is also an angle with a first arm 37 and a second arm 38 
joining at a vertex 39, but without an arcuate scale 15 as has been 
described in connection with the gauge 10. Here, however, the arm 38 
adjoins a connector 40 which has a receptacle 41 receiving the arm 11 and 
provided with a cut-out 42 through which the compass 33 can be viewed. 
When the arm 11 is inserted into the receptacle 41, the holes 22 and 23 
align with holes in the receptacle 41 and are traversed by pins 43 and 44 
to lock the attachment 30 to the gauge 10. In FIG. 6, the arm 45 is shown 
to be swung into its open position about a bolt provided with a wing-nut 
46. 
The closed position of the device is shown in FIG. 7 where the arm 45 lies 
along the arms 38 and 12. 
In use, with the extended arm 45, the device is brought to lie against the 
trunk of a tree (FIG. 8), bearing upon the arm 45 and the arm 37, in such 
a way that the needle 13 (sighting pin) lines up with or is parallel to 
the right side of the tree trunk. The reading is taken on the upper scale 
15. The value thus read is doubled to provide the diameter of the trunk of 
the tree. 
Of course, when smaller diameter trees are to be measured, the attachment 
30 can be removed by simply pulling up the pins 43 and 44 and the gauge 10 
can then be used directly to measure a trunk of the tree as shown in FIGS. 
12-15. The device is placed on the back of the hand (FIG. 12) which can 
pass through the loop of the rubber band. The arm 16 is swung outwardly 
and the thumb-screw 68 is tightened, utilizing the pin 13, a reading is 
taken as has been shown in FIG. 13 along the scale. The provision of the 
compass directly within the gauge allows orientation of the gauge with 
respect to the compass directions, i.e. the arm 18 in the north-south 
direction. 
As can be seen from FIG. 12, while the rubber band in the case of FIGS. 1 
and 2 is knotted in the holes 22, 24 to retain the band, a knot is 
provided at 50 in the device of FIG. 12 while the other end of the rubber 
band is held in place adjustably under two clamping bars 51, 52 on the 
upper side of the gauge. The clamping bars prevent withdrawal of the 
rubber band from the opening 24. The measurement of the diameter is 
obtained from the points A.sub.1, A.sub.2, A.sub.3 in FIG. 2, representing 
the contact points along a sector angle which has been designated at 
.sigma. is spanned between the three contact points A.sub.1, A.sub.2, 
A.sub.3. The sector angle depends upon the chest-high diameter of the 
trunk of the tree to be measured and amounts at a BHD of 30 cm to 
131.degree., a BHD of 60 cm to 102.degree. and a BHD at 90 cm to 
87.degree.. With a BHD of about 83 cm, the measured angle is practically 
exactly a right angle. 
Reference can be made to FIG. 14 which shows that with the aid of the 
compass, measurements can be made in four directions each 90.degree. 
offset from one another on a trunk which deviates from the circular. The 
results yield four diameters, each of which is assumed to cover a quarter 
of the cross section and can be added. From the total area, an average 
circular diameter can be calculated. 
FIG. 15 shows that for each of the 16 contact points corresponding to a 
succession of equispaced measurements taken about a tree, there is a 
simple relationship between the segment height h and the radius r or the 
diameter 2R. The calculation can be made by a relatively simple computer 
program. To enable the compass to be observed during the measurement from 
all positions, a small mirror may be mounted on the gauge to allow viewing 
of the compass. 
FIGS. 10 and 11 show that the gauge of the invention can be used, apart 
from its main function as a measuring device for trunk diameter at chest 
height, also for angle count sampling as has been described. The upper 
scale here is provided with a band 60 (FIGS. 10 and 11) which has two 
boundaries V, V, spaced apart by a third of the inter-eye spacing a, i.e. 
a third of the center-to-center distance between the eyes represented at R 
and L in FIG. 11. 
When this distance relationship is followed, using a spacing from the 
needle V from the scale surface of v, the detection of separate images by 
the right and left eyes of the regions V bounding this strip 60 will 
correspond to a given span in which a count can be effected in a manner 
analogous to that obtainable with a Relaskop.RTM.. More particularly, the 
eye spacing of the individual is used for obtaining a desired eye distance 
from one or more width marks on the scale surface. When the individual eye 
spacing a coincides with the double image of the needle V at the limits V 
of the band shown at 60, the eye is at a distance 3v from the needle V 
which, as noted, is spaced by V from the scale surface. The eye distance 
from the scale is thus 4v. At this distance an accurate count can be made 
which is reproducible by eye and without other equipment.