Calculator simulations

Charlie Carothers csquared3 at
Wed Dec 8 14:56:45 CST 2010

On 12/8/2010 8:55 AM, Rick Bensene wrote:
> Charlie C. wrote:
>> With the decimal point position set to blank, it did seem to get stuck
>> looping in state 31 forever when I divided 1 by 3.  It could also be
>> that I have no experience whatever with this calculator and this
>> behavior is quite normal. :-)  I found it curious that the only +
>> function is to memory, and I found the M+ and MR operation to not be
>> intuitive but that's probably just my ignorance as well.  Again, this
>> was with the DP position blank; maybe that is just not intended or I
>> don't understand it's purpose.
> The blank position of the decimal point setting switch does cause odd
> behavior in this class of machines.  Why Sharp (who designed the guts
> for many Facit calculators of this time) put a rotary switch in with a
> position that led to incorrect operation isn't clear.  Similar Sharp
> machines exhibit the same behavior.
> The really cool thing about Brent's simulations is that they are so
> accurate that they properly reproduce this behavior.  Brent's
> reverse-engineering skills are truly epic.
> To add, the "=" key is used.  Enter a number, press "=".  It is added to
> the display.  For example, to add 16 to 45, enter 16, press "=", enter
> 45, press "=", and the answer is in the display.  To subtract, just
> enter the number to be subtracted, and press the "-" key.  For example
> to subtract 9 from the result, simply enter 9, then press "-".
> Brent's simulation of the Facit 1123 does add the memory function keys
> that don't actually exist on the Facit 1123 model.  The circuitry is all
> there for the memory functions, but on the actual machine, the keys
> weren't on the keyboard.  A different model (that cost more) included
> the memory keys.  The memory is a separate register that can be added to
> or subtracted from.  The M+ and M- keys add or subtract the number in
> the display from the memory register.
> The CM key clears the memory register, and the MR key brings up the
> content of the memory register into the display.
> Rick Bensene
> The Old Calculator Museum
Hi Rick,
Thanks much for the explanation.  I notice that the Toshiba BC-1212 has 
one key labeled with both + and = so I'm guessing this was pretty common 
in that time frame.

The CM, M+ and M- do seem very intuitive to me as long as the DP switch 
is not set to blank.

BTW, my bad on Firefox, as I had failed to restart it after downloading 
and installing Shockwave.  After a restart the simulation works just 
fine with Firefox.
Charlie C.

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