When batteries run out, what machine can perform fast calculations as efficiently as your calculator, that it is the preferred counting tool by many merchants the world over even in the modern age of pocket calculators and mobile computers?
It has been proven that abacus calculation techniques are one of the fastest ways of doing counting or any standard arithmetic from subtracting to multiplying and dividing, especially when it comes to large numbers. Children love to play, and teaching them how to use the abacus helps them learn how to count while having fun moving all those beads around. Teaching kids how to use one will help them perform math calculations visually, when they need to compute and have no tools at hand. Ain't that ingenious? It usually takes from 3 to 6 months of constant practice, until using the abacus becomes second nature.
Modern Abacus with beads for resetting values. Gisling for WikiCommons CC BY 3.0
Mastering the abacus and learning visual mental arithmetic techniques also aids in working memory skills and you get more than just using flash cards. Working with one helps you keep a more focused mind and better concentration on problem solving, as well as patience as you move the beads around to arrive at a sure answer, instead of remembering a flash card value to solve your problem.
An abacus stimulates the brain by using the sense of sight, and touching. Forget that stupid crap teachers heap on young kids who use their fingers to count, telling them it's the wrong way to learn. Counting with your fingers (simulating an abacus in your mind) for large number problems is actually faster than jotting them down on paper and 'doing the math.'
The Soroban or Japanese Abacus, this one a modern version. Maksim for WikiCommons CC BY-SA 3.0
People can learn math faster with this incredible tool. In the age of electronics, many often sneer at Chinese or Arab merchants who use an abacus as an archaic method, but a calculator may break down after heavy use and might not be as accurate if its buttons are worn out. Not to mention, batteries eventually run out.
If you are running a business that keeps an inventory, having one or more of these counting tools will not only help you keep track of everything, along with a ledger, but also help keep costs down—you don't really need that expensive POS system if you can run everything just using an abacus, your ledger books, and some printed receipts.