Using a VRuler for 10 Combination
Division
The one tool unique to
temarimaking is a Vruler. They are great little gadgets that are
simple to use as one method for placing the pins for a 10 Combination
Division. They are supplied through the Japan Temari Association in
Tokyo; the JTA agreed to allow them to be
offered
through Temarikai, in good faith only at the cost of
purchase/shipping from the JTA (supplies and related items sold
through the JTA and Temari Museum are what help to provide the operating
funds for the Association).
A Vruler is a flexible plastic device shaped like a
V, with the inside of the V cut to the required angle of 72 degrees.
Each leg has a metric measuring rule printed on it, hashed in mm and cm
with an arrow on the 5cm (50mm) mark. Using a Vruler eliminates
the need the paper strip when setting up a C10, and is a quick, direct
way to mark the mari. You need only know the
circumference
in cm. For those not comfortable with using metric units  you
will want to for this division. Once the circumference in cm is known,
you then determine the VRuler value for that measurement. It is an easy
calculation but, a simple reference chart eliminates the need to
calculate values for most standard mari sizes.
For reference, the formula is
an easy threestep process. For the nonmath folks: divide the
circumference (measured in cm) by 6, and remember that result (call it
Result A). Divide the circumference by 100 and remember that result
(call it Result B). Add Result A and Result B together, and you
have the VRuler value you need for your mari. For the math folks, it's
written as (circum/6)+(circum/100)=Vruler value.
The VRuler value, is the distance
between the centers of the pentagons on a C10, and each pin placed for a
C10 marking will be this distance apart; any 3 points will be oriented
on 72 degree angles from each other along this distance. Thus, each pin
placement is a center of a pentagon. If you multiply the distance
between the centers (Vruler value) by 0.679, and you will get the
length of the side of the pentagons, which some people fine useful for
when you are adjusting the marking threads into final placement before
tacking the intersections.
Here is the basic method for using the Vruler:

Measure the circumference in
cm. This example is 27 cm. Once the circumference is
determined, use a Vruler reference chart (below) to determine
the Vruler value. Look up 27 and the Vruler Value is
4.8. Or, using the formula (which, if you are
using a paper strip, you must do), the standard
calculation of (27/6)+(27/100) = 4.77. Round to the
nearest tenth cm so 4.77 rounds to 4.8. Either method works
(!). 

Choose any point to be the
temporary North Pole and place a pin. Hook the inside of the
angle of the Vruler on the pin, flatten one leg of the ruler
along the mari and place a pin (Pin 1) at the Vruler value
(here it is 4.8). Note that a C10 division does not have north
and south poles, it is fully 3D symmetrical when completed,
but to start the process we need to set a temporary one to
make it easier. 

Flatten the opposite leg of the
Vruler on the mari (without "stretching" or "closing" the
angle), and place the second pin (Pin 2) at the Vruler value
on the second leg. Note that the "back tab" of the ruler,
behind the NP pin, is NOT flat on the mari; only the legs of
the ruler are. If you remove the Vruler from the NP pin and
use it to measure the distance between Pins 1 and 2, it should
be the same. It's very common, even with experience and
practice, that the last placed pin will need to be adjusted a
bit; check and adjust as needed. Remember that this number is
the distance between centers, and you are pinning the centers
of the 12 pentagons on a C10 Division; they need to be
accurate. 

Pivot the Vruler around the NP
pin and place the right leg against Pin 2. Flatten the ruler
and place Pin 3 at the Vruler value on the left leg. Try to
be sure to not "stretch" the ruler out of shape, don't pull
the legs apart. The tab behind the angle pin will not lay flat
on the mari so don't try to force it, but the legs should be
flat on the surface. Remember to check the distance between
Pins 2 and 3, and adjust if needed, & adjusting is usually
always needed. The VRuler needs to be flexible to work.
Adjusting is part of using the tool. Remember too, within 12
mm is fine. 

Continue pivoting the Vruler
around the NP pin until you have placed five pins around the
NP. You now have six pins all spaced the same from each other,
which is the Vruler value, which is the distance between
centers of a C10 Division on this particular mari size. You
can check your pin placements by removing the Vruler and
aligning it against any 2 pins, one of which is in the inside
angle. Adjust any pins as needed. 

Remove the Vruler from the NP and
"hook" it on any other pin, here Pin 3 (which becomes the new
temporary NP). Lay the right leg against Pin 2, flatten the
left leg to place Pin 6 using the Vruler value, just as you
did for all the previous pins. Pivot around Pin 3 as it is the
"new, temporary" NP and continue. 
As mentioned above, one need not sit and crank out the center
distances (Vruler value) for each mari size; these charts are
readily available in many Japanese books and other sources, as
well as here. Keep a copy in your stitching kit along with a
Vruler and you're good to go.

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