Abacus Fun
Carol Peterson
(Math)

Building a Chinese abacus is a fun way to work with wood AND practice math!  For each abacus you will need the following:
    One 6” x 12” piece of wood (½” – ¾” thick)
    20 nails 1” long or longer
    50 beads of one color with large center holes.  We will use blue.
    20 beads of a second color with large center holes  We will use yellow.
    Wire that will fit through the bead holes  
    Sandpaper    
Hammer
    Wire snips or scissors
    Felt pen
    Ruler
    Paint or stain – if desired
First, sand the edges of the wood smooth.  The wood can be painted or stained, if desired, but should then be left to dry before proceeding.  
Using a ruler, draw three horizontal lines across the wood, 1” from the top edge; 3” from the top edge (marking the center of the wood); and 1” from the bottom edge.
Starting 1” from the left side edge, hammer a row of ten nails along the top line, spaced 1” apart, leaving about ½” between the wood and the head of the nail.  
Hammer a second set of 10 nails on the bottom line, starting 1” from the left side, trying to line up the bottom and top rows of nails.  Hammer the nails into the wood about ½” so that there is plenty of space between the wood and the head of the nail.
With the felt pen, write the numbers 1 – 10 from right to left on the wood below the bottom row of nails, so that each nail has a number.  Then write a “1” below the center line and a “5” above the center line.
Cut 10 pieces of wire, each 8” long.  Wind the wire twice around bottom nail #1.  Slide 5 blue beads onto the wire.  Then slide 2 yellow beads onto the wire.  Stretch the wire and wind it onto the top nail of row #1 until the wire is tight.  Repeat with all ten wires so that all ten rows of nails contain a wire with 2 yellow beads on top and 5 blue beads on the bottom.  Push the wires towards the head of the nails so that the beads slide easily.
Now you are ready to use the abacus!

Parts of the Abacus

The Lines:  The center horizontal line on the wood is called the “beam”.  The part of the abacus below the beam is the “lower deck”.  The part of the abacus above the beam is the “upper deck”.  

Bead Value:  Each bead has a number value.  Starting from the right, the row of beads at nail #1, is the ones column.  The next row of beads at nail #2 is the tens column.  The next row of beads, at nail #3 is the hundreds column.  Then is the thousands and so on.  This abacus can be used to count numbers all the way to 10,999,999,999.  

Above and Below the Beam:  Each blue bead below the beam counts as one unit (one blue bead below the line in row #1 equals l; one blue bead below the line in row #2 equals 10; one blue bead below the line in row #3 equals 100, and so on).  

Each yellow bead above the beam counts as 5 units.  (One yellow bead above the beam in row #1 equals 5; one yellow bead above the beam in row #2 equals 50, and so on).  

Using the Abacus

Start by moving all of the blue beads towards the bottom nails and all of the yellow beads towards the top nails.  You count by moving beads towards the beam.  For example, to show the number 15,637:
•    Move two blue beads and one yellow bead towards the beam in the row #1 (to show the number 7).  Keep the rest of the beads in that row next to their nails.
•    Move three blue beads towards the beam in row #2 (to show the number 30).  
•    Move one blue bead and one yellow bead towards the beam in row #3 to show the number 600).  
•    Move one yellow bead towards the beam in row #4 (to show the number 5,000).
•    Move one blue bead towards the beam in row #5 (to show the number 10,000).  
•    Unused beads in all columns are pushed towards the nails.
After you have practiced making numbers on the abacus, try playing games with a partner to see who can solve addition and subtraction problems only using the abacus.  To do this, enter the beginning number on the abacus and then add or subtract beads to equal the second number.

Approximate building time:  20-25 minutes (plus painting or staining)