Calculator simulations

[Tony Duell]

> 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.

A number of machines had keys labelled '+=' amd '-=' or something 
simialr. Addition and subtraction were effectively RPN : 

2 + 3 = -> 2 += 3+=

7-5 = -> 7 += 5 -=

Multipliciation and division used normal infix notion with the '+=' key 
being used for the 'equals'.

The Casio AL1000 (Commodore AL1000 in the States I think) and I believe 
the AL2000 had something slghtly weirder. They used the += and -= as 
above for addition and subtraction. Multiplication were infix, using += 
to give all digits of the product/quotient and -= to round it to the 
number of digits set on the decimal places thumbwheel. There was also a 
swtich for 5/4 rounding or truncation.

-tony