Make a pocket abacus from an empty Altoids tin. The original low-tech calculator, now in pocket size! Great for calculating tips in restaurants, as long as your check isn't more than a million dollars.

Step 1: Materials

Materials needed:
Empty Altoids tin
small colored beads
wire
an awl

Optional: spray paint, craft paint

Step 2: Step One: Poke Holes

This abacus will have 9 columns (9 digits). You can calculate up to 9,999,999.99 if you use decimals, or up to 999,999,999 if you only use whole numbers.
For this you will need to poke 9 holes, to string 9 wires.

First use a sharpie marker to mark where your holes will go.
Mark them on the long sides of the Altoids tin.
Start with the center hole (the 5th hole)
Then you can mark 4 holes to the left and 4 to the right. try to keep them evenly spaced.
Then repeat the process on the other long side, making 9 more dots with your sharpie.

Now, use the awl to poke the holes in the tin. Try to poke as small a hole as possible, so just the tip of the awl goes through.
Poke all 18 holes.

Next you will need to poke 2 holes on each of the short sides of the tin. This is for the "divider" wire which separates the Heaven beads from the Earth beads. The divider is perpendicular to the columns, and is located about 1/4 of the way from the top.
The distance between the top of the tin and the divider should be at least the diameter of 3 of your beads. The top 2 beads need room to move.

Step 3: Optional: Paint the Tin

An optional step is to paint the Altoids tin.
I spray painted mine black.
You may also want to paint the inside or glue a piece of light colored paper to the inside bottom.
This light backing just helps you to see the beads more easily.
I painted the inside bottom of my abacus in a pale matte grey, using acrylic craft paint.
You can also just cut a piece of light paper the shape of the tin, and glue it into the bottom.

Step 4: Step 2: Start Stringing the Wire.

I find it easiest to start stringing at the bottom right corner.
Cut a piece of wire 36 inches long.
Thread the wire through the first and second holes in the bottom right corner, and tie it off on the inside of the box.
Next, you will string 7 beads on the wire. the bottom 5 will be your earth beads and the top 2 are the heaven beads.
I used different colored beads for earth and heaven, but they can also be the same color..

After you have the correct 7 beads on the wire, then string the end of the wire through the first hole in the upper right corner.
Next, String the end back down through the second hole in the upper right corner.
Now you will again string 7 beads on the wire, but this time you string the heaven beads first and then the 5 earth beads.. (if you are using contrasting colors).

Step 5: Step 3: Continue Stringing

Continue to string the wires and the beads in the successive holes, from right to left.
Make sure to keep 7 beads on each wire and to keep the 2 heaven beads on the top edge.

I have also changed colors for the earth beads, to mark the Unit columns.
This is a feature more commonly seen on Japanese abacus, but I've added it to this Chinese style abacus because it's useful.
My two columns on the right have blue earth beads, these are the decimal places. (tenths and hundredths)
The other 7 columns have green earth beads, for whole numbers.
The third column from the right is marked with a black bead, and this will be repeated on every third column.
These mark where decimal points and commas would go. it's just a quick visual reference to separate the columns.
For example in the number 53,008.75, the 3 and the 8 would be in Unit columns because they are followed by a comma or a decimal point. Those unit columns are marked with a black bead.

Step 6: Step 4: Adding the Beam

Last, you need to add a divider between the heaven beads and earth beads. This is called the beam.
I've used a thicker wire for the divider, string it through the holes in the shorter sides, and go UNDER the wires with the beads on them.
Then poke the wire through the opposite hole, and tie it off on each side inside the box.
The beam wire should be taut and touching the column wires, which will prevent the heaven beads from sliding down into the earth bead area.