Using C10 Ruler for Jyuttoubu no kumiawase /10-Combination Centers

While the V-Ruler has been a long-standing standard for placing centers for a Jyuttoubu no kumiawase /10-Combination Division, there is an alternative. Like the V-Ruler, it is more conversion gauge than ruler; the markings on it represent the distance between C10 centers against the mari circumference in cm represented by the numbers. Thus, it converts the circumference of the mari to the distance between the 12 centers of a C10. It can be easier to manage than the V-Ruler, since it eliminates the "wiggle factor" when flattening the V-ruler on the mari.

Using the C10 ruler (rulers are available here) requires first pinning the centers for a Simple 4 marking. These 6 centers will then be used to place the ruler and identify the 12 centers of the C10. After placing the pins for the C10 centers, the Simple 4 pins are removed. The marking lines for the C10 can then be laid down using whatever method is preferred.

When placing the ruler on the mari, it will be centered on a Simple 4 pin. Be sure to use the extra length of the ruler to extend to the adjacent pins to insure that it's place on a straight line, either horizontally or vertically as required.

To begin: Determine the circumference of the mari, and then pin the 6 4-point centers of a Simple 4 division by whatever method you prefer. Then use the C10 ruler as follows:

 Locate temporary N & S  poles. Center the ruler on an equator pin. The circumference of this example mari is 23cm. Place pins at the 23 marks on either side of the 00-point. Rotate the mari 1/4 turn to the right; lay the ruler vertically (be sure to align straight). Place pins at the 23 marks. Rotate the mari 1/4 turn, lay the ruler horizontally, place pins at the 23 marks. Rotate the mari 1/4 turn, lay the ruler vertically, place pins at the 23 marks. Locate N-S line; there are no pins on it at this point.

 Center ruler on N pole, place pins at the 23 marks. Rotate mari 180 degrees to S pole, center ruler and place pins. Remove S4 pins. Place C10 lines using preferred method.