Very simple and informative site regarding the Abacus. I have never actually used an Abacus so I found the site to be interesting. The general explanations and intructions on how to add/subtract using the Abacus were good. I spent about 20 minutes reading the site and trying the Abacus. As far as a teaching tool, if for some reason I needed to explain how to use the abacus or give a demonstration of what an Abacus is I would definitely reference this site because it is brief and concise. I think that anyone could learn using this site.
My computer did not have Java Virtual Machine installed so I had to download it and install it prior to viewing the online abacus.