## An Abacus that works!!!!!!

Those of you that have read previous posts on Abaci (Here and here) will realise that I have been on the lookout for one that works in our base 10 society. All the simple abaci that are available seemingly anywhere in the country have 10 beads per line, but this doesn’t work. You move zero beads for zero, one for one etc and then when you get to ten you move the nine back and one from the next row across. These ten bead abaci have a bead on each row that will never move!

Today I took my daughter to one of the local parks, as she was playing on the slide I looked across the park and noticed this:

I was in a state of shock, at first I couldn’t believe my eyes, so I went for a closer look, and sure enough, there it was. An abacus with 9 beads per row. Finally one that makes sense in this society!! well done Leeds City Council.

How about a soroban? Modern versions have only 5, not 9 beads, for each place. One of the 5, the “heaven” bead, is worth 5; the 4 “earth” beads are worth 1 each.

Aye, they’re based on the roman numerals I think. She’s only 21 months though, start with base ten first…..

Have you seen these?

http://www.amazon.co.uk/Wooden-Framed-9-bead-Counting-Education/dp/B00AHT07ES

Ebay sell the same ones too.

Haha, yes i saw them just before xmas and bought one!

You say the tenth bead will never move but it does. I came upon yr article because like you I wondered why my child’s abacus had ten beads not nine. If using an abacus to record numbers you only need nine but to do arithmetic it’s much easier if it has ten. Try the sum 9998+3 with both types and you’ll see why. I see from Wikipedia that all historic abaci have ten (or 5+2) excerpt Roman and Japanese which both have 4+1 or 4+2. Cheers. Nick

Surely if its for that reason it should have 19?! The 5+2 and 4+1 are both interesting concepts and work well.