This abacus is showing the value 5402. Moving beads towards the horizontal divider adds that value, moving beads away clears the value.
The Chinese abacus was brought into Japan around the 17th century (Rentchz). It was studied by the Japanese mathematician Seki Kowa (1640 - 1708) and many refinements were made to the Chinese abacus, including removing one bead on each wire above and below the horizontal dividing bar. The transformation of the Chinese abacus into the modern Japanese form was completed by 1920 (Kojima 25). This modern form has 4 beads below the horizontal divider, and only one bead on each wire above. It also usually has 21 columns (Fernandes).
The Russian abacus is similar in form to the Chinese or Japanese abacus, and was probably brought to Russia from China. The Russian form is set up to do calculations in rubles and kopeks. It has no horizontal divider, but some of the beads on each wire are a different color, to help as place-keepers (Pullan 100). Older Russian abaci have some additional columns for quarter kopeck as well as quarter ruble values (Leipala). If you go to Russia today, you will still see the abacus used. Ed Oswalt made this observation when he went to Russia in 1997: "The same store . . . where you can buy a Pentium computer, computes your bill using an abacus."
An interesting form of the abacus was found during archeological excavations in Central America. This abacus dates to around 900 AD and is constructed from maize kernels threaded on a string, all contained within a wooden frame (Fernandes). Grado states that an abacus of this form would have 7 beads by 13 columns.
Math on the Counting Table
Simple mathematical calculations on either the abacus or the counting table are pretty much the same as pen and paper sums, but instead of using abstract representations of the quantity, you use counters or beads to represent a quantity, and position to represent value. If you were to add up two sums of money by sorting each pile out by denomination, then adding the pennies of the first pile to the pennies of the second pile, the nickels of the first to the nickels of the second, and so on; and also normalizing as you go (5 pennies are replaced by one nickel, 2 nickels by one dime, etc.) you would get a good feel for addition on the counting table.
Subtraction on the counting table depends upon the idea that you can represent larger sums of money in more than one way: 10 cents as one dime, or as 2 nickels, or as 10 pennies, or even as 1 nickel and 5 pennies! Of course, the pennies would be represented by counters on the penny line, and nickels by counters on the nickel line, etc. For subtraction, you have to make sure that the number your are subtracting from (minuend) has no fewer counters in each unit than the number you are subtracting (subtrahend) (Moon 28).
has a diagram of subtraction on the counting table.
Division can be done on the counting table as though you were doing standard long division. However, that is not how it was done in Medieval and Renaissance Europe. Modern long division on the counting table is a difficult operation, even though it is only repeated subtraction. It is a long, tedious process made a little easier if you can factor first and then divide. It is useful to keep a tally of how many subtractions have been done. Multiplication on the counting table, at least in medieval Europe, was NOT done as we do today - it used the processes of mediation and duplation to find the product of two numbers. If you did not know what 13 x 6 was, this is how you would find the answer:
Make two columns beginning with the numbers you want to multiply. Repeatedly halve the values of the first column (toss out remainders) and repeatedly double the values of the second column. For each even value in the first column discard the matching value in the second column. Add the remaining second column numbers up for your answer (Moon 54).
13----6
6----12
3----24
1----48
discard 12 from the second column, leaving 6, 24, and 48.
6+24+48=78 or 13x6=78
Math on the Bead Abacus
To do simple arithmetic on the bead abacus, you first must determine what base you want to use, and if you want to have fractional values available. Dave Bernazzani gives this very concise explanation of a base 10 numbering system for the abacus:
One of the columns is chosen to be the "Units" column and can be any column of your choosing (if you are working with only whole numbers, simply use the rightmost column). If you are working out calculations for monetary sums - reserve the rightmost 2 columns for the decimals and make the 3rd column the "Units" column. Each column to the left of the units column is worth 10 times more than its right-hand neighbor. Each column to the right is worth 0.1 times its left-hand neighbor. So, for example, if you choose the third column to be the "Units" column then you would have the following values:
First Column: Hundredths
Second Column: Tenths
Third Column: Units (Ones)
Fourth Column: Tens Fifth
Column: Hundreds
Sixth Column: Thousands Etc.
(Bernazzani).
An everyday use for the abacus is adding numbers together as you would in a shop. The basic idea of addition is to enter one number into the abacus and then add the second number, column by column, to the values that are already in each column. Although you can work from left to right or right to left, it is more efficient to work right to left (move fewer beads). The only tricky part of addition is when you do not have enough unused beads in that column to represent the value you want to add. Subtraction is just the reverse of addition, with the same necessity of sometimes subtracting 10 and adding 1 in order to take away 9 (Dilson 43ff). and show the basis of addition and subtraction operations.
Simple multiplication (i.e. 5 x 7) is done as repeated addition. It is useful to keep a running tally of how many times you have added 7. The unused columns on the left hand side of the abacus can be used for this. Two digit or higher multiplication is done just as with pencil and paper. It requires memorizing the times tables or having a second abacus to do the simple multiplication. The units column is done first. The results of the multiplication of the unit of the bottom number and the tens of the top number are stored IN THE SECOND column. Keep in mind the process of pen and paper multiplication, and the abacus presents no real difficulty. Division is done as repeated subtraction - again keeping a tally of how many times you have subtracted (Dilson 121ff). Figures 4 and 5 illustrate these 2 processes.
If you would like a little challenge, try doing calculations in other number systems. The Chinese abacus is already useful for base 2 and base 16 calculations. Each rod on the Chinese abacus has 16 possible values because that was the unit of weight in China (Accent Interactive). Because of this, you can also use the Chinese abacus for hexadecimal calculation. And if you ignore the earth beads, you can use the heaven beads for binary calculations.
The best way to learn about the abacus is by doing. Get a stack of pennies or buttons, clear a spot on the kitchen table and try out some sums! And as you are busily calculating away, keep in mind that you are continuing a two thousand year tradition that is still alive and well today.
Figures
Figure 1: Subtraction of 7 from 15 on the counting table
Step One
------------------+---------------- Thousand
|
------------------+------------------
|
--------------O---+------------------
O | O
------------------+--O-O------------- Unit
value of 15 value of 7
Step Two
------------------+---------------- Thousand
|
------------------+------------------
|
------------------+------------------
O O | O
--------O-O-O-O-O-+--O-O------------- Unit
value of 15 value of 7
Step Three
------------------+---------------- Thousand
|
------------------+------------------
|
------------------+------------------
O O | O
--------O-O-O-O-O-+--O-O------------- Unit
Remove counters that cancel each other out
Step Four
------------------+---------------- Thousand
|
------------------+------------------
|
------------------+------------------
O |
------------O-O-O-+------------------ Unit
Final answer is 8
Figure 2: Adding 9 to 8 on the Chinese abacus
Step One
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | | O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Begin with 8 in the units column
Step Two
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | O O ||
|| O O O O O O O O O O O | O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Add 10 to the tens column
Step Three
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | O O ||
|| O O O O O O O O O O O | O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Subtract 1 from the units, giving answer of 17
Figure 3: Subtracting 9 from 27 on the Chinese abacus
Step One
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O | | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
enter value of 27
Step Two
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | O O ||
|| O O O O O O O O O O O | O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Subtract value of 10
Step Three
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | O O ||
|| O O O O O O O O O O O | O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Add value of 1 for answer of 18
Figure 4: Multiplying 68 by 7 on the Chinese Abacus
Step One
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O | | ||
|| | | | | | | | | | | | O O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | | O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
8 x 7 so 56, so put 6 in units column and 5 in tens column
Step Two
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O | | ||
|| | | | | | | | | | | | O O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | O O O ||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O | O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O | O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
7 x 6 is 42, so add 2 in tens column and 4 in hundreds column for final product of 476
Figure 5: Division of 15 by 5 on the Chinese abacus
Step One
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| | | | | | | | | | | | O | ||
|| O O O O O O O O O O O | O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Put 5 in units column and 10 in tens column
Step Two
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| | | | | | | | | | | | | | ||
|-------------------------------------------|
|-------------------------------------------|
|| O | | | | | | | | | | O | ||
|| | O O O O O O O O O O | O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Take 5 away, and add a marker bead on far left
Step Three
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O | ||
|| O O O O O O O O O O O O O ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| O | | | | | | | | | | | | ||
|| | O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Convert 10 to 5+5
Step Four
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O | ||
|| | | | | | | | | | | | | O ||
|-------------------------------------------|
|-------------------------------------------|
|| O | | | | | | | | | | | | ||
|| O O O O O O O O O O O O O ||
|| | O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Take 5 away, and add a marker bead on far left
Step four
+-------------------------------------------+
||-----------------------------------------||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| | | | | | | | | | | | | | ||
|-------------------------------------------|
|-------------------------------------------|
|| O | | | | | | | | | | | | ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| | O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
|| O O O O O O O O O O O O O ||
||-----------------------------------------||
+-------------------------------------------+
Take 5 away, and add a marker bead on far left for a remainder of 0 and a tally of 3
References
Accent Interactive. "Chinese Abacus"
http://www.accent.co.uk/chinabacus.html: 28 March 1999
Bernazzani, Dave, "Chinese Abacus and Japanese Soroban",
Dave Bernazzani's Home Page http://www.tiac.net/users/dber/abacus.htm: 28 March 1999.
Dilson, Jesse. The Abacus: a Pocket Computer.
New York: St. Martin's Press, 1968.
Feibao, Du. "Abacus, the Earliest Calculating Machine in the World", The China Experience http://www.chinavista.com/experience/abacus/abacus.html: 27 March 1999.
Fernandes, Luis. "Introduction", The Abacus, the Art of Calculating with Beads http://www.ee.ryerson.ca:8080/~elf/abacus: 28 March 1999
Grado, Victor M. "Nepohualtzitzin, A Mesoamerican Abacus" http://www.ironhorse.com/~nagual/abacus: 28 March 1999
Kojima, Takashi. The Japanese Abacus: Its Use and Theory. Tokyo: Charles E. Tuttle, 1954.
Leipala, Timo. "Russian Abacus (Schoty)", http://www.dotpoint.com/xnumber/pic_abacus3.htm: 2 April 1999
Moon, Parry. The Abacus: Its history; its design; its possibilities in the modern world. New York: Gordon and Breach Science, 1971.
Pullan, J.M. The History of the Abacus. London: Books That Matter, 1968.
Oswalt, Ed. "Ridiculous Observations In Russia" http://www.jao.com/ace/ruslist.html: 28 March 1999
Rentzsch H., G. Ottenbacher. "History of Computing" http://wwwstall.rz.fhtesslingen.de/studentisches/Computer_Geschichte/grp1/seite2.html: 28 March 1999