The earliest counting device, developed by Babylonians in 300BC, was made of marble and used by manipulating pebbles inside carved grooves. Early Romans added more grooves, modifying the device correspond to their numerals I, V, X, L, C, D and M. Today's abacus most closely resembles the Japanese soroban, which emerged during the 15th century. It is composed of 13 parallel rods containing beads and housed inside a rectangular frame.
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Reading from right to left the first four rods represent decimals. Successive rods represent ones, tens, hundreds, thousands and millions. The abacus also contains a horizontal reckoning bar. Heaven beads, those above the bar, represent 5 units each, while earth beads, those below the bar, represent 1 unit each. The soroban contains 1 heaven bead and 4 earth beads, giving each rod the capacity for 9 units---just like today's calculators.
Clear the abacus by allowing gravity to force the earth beads down, and push the heaven beads upward. The abacus is now zeroed out and ready to use.
Add 237 and 152 by first entering 237 into the abacus. On the ones rod pull down 1 heaven bead and push up 2 earth beads, representing 7. On the tens rod push up 3 earth beads, and on the hundreds rod push up 2 earth beads. Add 152 beginning again with the ones rod, pushing up 2 earth additional earth beads. On the tens rod, pull down 1 heaven bead, representing 50. On the hundreds rod, push up 1 earth bead, representing 100. Your abacus should now read 389.
Clear the abacus again to perform a subtraction problem. Begin by inputting 187. On the ones rod pull down 1 heaven bead and push up 2 earth beads, representing 7. On the tens rod pull down 1 heaven bead and push up 3 earth beads, representing 80. On the hundreds rod, push up 1 earth bead, representing 100. To subtract 125 begin with the ones rod. Push up1 heaven bead, subtracting 5. On the tens rod, pull down 2 earth beads down, subtracting 20, and on the hundreds rod pull down 1 earth bead, subtracting 100. Your abacus should now read 62.
Addition and Subtraction on a Japanese Abacus
Tips and warnings
- Ignore additional beads if working with a different type of abacus. For example he Chinese abacus, known as a suan pan, has more beads because it operates on a sixteen unit scale.
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