An abacus is a primitive calculator. There are
several Javascript/Java Abaci on the net, but this particular one
is especially suitable for learners because it contains a
history of the numbers you composed in the abacus.

The history box

After 2 seconds of inactivity the number shown on
the abacus is recorded in the history. After 7
seconds of inactivity, a separator is added to the history.

Clicking on a numeber in the history box copies it into the abacus.

Double-clicking a number in the history box also highlights it.

Fractions

You'll notice that every 3'rd rod (or every 4'th, if the
base is binary or hex), starting with the unit rod,
has its background lighted in yellowish hue. This makes it
easier for you to read "large" numbers. It has the same functionality as the
thousands separator's in our modern writing system.

Rods to the right of the unit rod denote the
fraction. By default these are the two rightmost rods. Click
on the digit printed bellow a rod to turn its rod into the
unit rod.

How to use it

How to use an abacus? There are two different reasons to use an abacus:

If you want to teach a kid about the way numbers are written, select
the simple "School" abacus. See Maria Miller's blog post.

If you wish to learn more about using the abacus, see this tutorial. Especially pay attention to
the "complementary numbers" principle.

Multiplication and Division

When doing multiplication and division, two extra abaci
are sometimes used.
to enable then.

Downloading

You may download this web page and use it on your own
personal computer. Either use the fancy "save as web archive
(single file)" function of your browser, or simply download
all the files form this folder. You may not
install this application on a public server (unless I
explicitly consent).

Problems?

This application was tested on Opera and Firefox. I did
run it under Internet Explorer ...and found some anomaly in
the history box (and slowness).