Using an Abacus/Basics
Types of Abacus
editThere are many sorts of abacuses from different times and places. In modern times, the ones most used are:
- The Chinese abacus, the suanpan. It may have 7, 9, 11 or 13 rods. Each column has 2 upper beads (quinary) and 5 lower beads (unary), separated by a bar passing through the abacus.
- The Japanese abacus, the soroban. 9, 11, 13, 15, 17, 21, 23, 25, 27, 29 or 31 rods. 1 quinary and 5 unary beads. Reference point.
- The modern soroban (since 1922, gaining popularity from 1945 onward). 9, 11, 13, 15, 17, 21, 23, 25, 27, 29 or 31 rods. 1 quinary and 4 unary beads. Reference point.
The above is a Japanese Soroban with a zeroing mechanism. By pressing the button two levers push the top beads up, and the other beads down, resetting the abacus.
The reference points allow the user to choose one rod as the base rod that counts multiples of one. This is very useful when calculating with decimal numbers or with numbers that end with zero.
This course uses the modern soroban with as many rods as necessary for the examples.
Unary and Quinary Beads and Activation
editThe unary beads are the lower beads, and they represent one unit each. The quinary beads are the upper beads, and represent five units each. Beads are counted when they are pushed to the central bar and are then said to be activated.
Representing Numbers
editThe numbers from 0 to 9 are represented as follows:
Soroban
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| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
Suanpan
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| 0 | 1 | 2 | 3 | 4 | 5 | 5 | 6 | 7 | 8 | 9 | 10 |
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| 10 | 11 | 12 | 13 | 14 | 15 | 15 | 16 | 17 | 18 | 19 | 20 |