# [IAEP] Abacus suggestions

Yoshiki Ohshima yoshiki at vpri.org
Sun Oct 9 14:20:07 EDT 2011

```  Hi, Walter,

At Sun, 9 Oct 2011 08:57:51 -0400,
Walter Bender wrote:
>
> >  - As you can see, the default 1's digit (the big white dots) is in
> >    the middle, not the far right.  That makes sense to tell that
> >    there are numbers smaller than 1 and for the idea of power of 10.
> >    (It is often a good technique to slide the decimal point, so I
> >    first thought the red triangle to mean this, but it is something
> >    else.)
>
> The red triangle is a mark found on many Chinese abaci. It is useful
> for to keeping track of place while doing multiplication and division.

Ok.  The scheme on the wiki is different from what I know.  Which
clears the used digits of multiplier as you go and that serves as the
tracker.  But I see that if you have it there, it can be used for such
a purpose.

> >  - For a non-"5 and 4" abacus, this is not simple, but then why kids
> >    in the 21st century need to learn Mayan arithmetic...
>
> My goal with the abacus was primarily to introduce the idea of
> multiple representations.

Ok...  It seems to me that these different traditional ones are tied
to the way they say or write numbers.  In other words, the abacus in
that culture feels natural, but once we try to map the numberto base
10 arabic notation, it requires some extra mind work.  Which may be

> >  - So, there are some 90 combinations of two one digit number
> >    additions.  Some require 5's compliment arithmetic (adding 4 to 2
> >    is subtracting 1 but then adding 5, etc.) or 10's (if it is the
> >    right terminlogy.)  Abacus was about building the muscle memory
> >    for these 90 patterns of additions.  Some of these require you to
> >    move both index finger and thumb at the same time.  After
> >    acquiring this muscle memory, you can do any additions without
> >    thinking, and that is the point of abacus.  But now, "doing
> >    additions without thining" is easier with electronic calculators.
> >    At the same time, the Abacus activity is not set up for learning
> >    build the muscle memory).
>
> I haven't played with the abacus on the touch-screen XO yet... but it
> is not multitouch. Muscle memory is not something we can do much with
> on that hardware :P

Hmm, too bad.  The real abacus as an artifact feels good.  We ride
on it like a skate board, too.

> > ----------------
> >
> >  - There is a bug when I tried to make my own abacus.  If there is a