The Museum of HP Calculators

HP Forum Archive 07

[ Return to Index | Top of Index ]

Mystery Calculator (semi RPN?)
Message #1 Posted by aruid on 17 Feb 2002, 9:58 p.m.

I recently found a interesting calculator. It is covered with sheet aluminum and has a green LED display it reads "Unisonic 890" on the housing. Upon putting in 4 AA batteries and turning this calculator on I noticed something unusual. I type [9] [X] [9] [=] and it reads "81", If i type [9] [/] [3] [=] it reads "3", thats normal. But typing [6] [-] [3] [=] it reads "-3"

If I type [6] [=] [3] [-] it reads "3" I only works correctly if I put in the multiplication and division algebraically and input the addition and subtraction using RPN.

What the heck? Was this calculator designed to do this? or is it broken? If it is "broken" I want to "brake" it more so the multiplication and division is RPN too!


Re: Mystery Calculator (semi RPN?)
Message #2 Posted by Ernie Malaga on 18 Feb 2002, 12:36 a.m.,
in response to message #1 by aruid

From what you tell us, it seems like this calculator uses "adding machine logic" like the HP-10A did many moons ago. In the HP-10A, the += key (the same key for both functions) was used to either complete a pending multiplication or division, or to keep accumulating numbers (adding them).

If the calculator you have follows that logic, then the = key must be accumulating, and that's why 6 - 3 = gives a -3: you're subtracting 6 (6 -) and then adding 3 (3 =), giving a net result of -6 + 3 = -3.

On the other hand, perhaps the calculator is just broken. 8^)

Re: Mystery Calculator (semi RPN?)
Message #3 Posted by db(martinez,california) on 18 Feb 2002, 12:25 p.m.,
in response to message #2 by Ernie Malaga

i think ernie is right. a lot of early to mid 70's calcers used exactly that type of logic. some had keys marked += and -= and most of these had no = key. a real weird one was the sears M8. you could switch the = key to be a % key. and they said rpn is strange.

[ Return to Index | Top of Index ]

Go back to the main exhibit hall