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On 2015-07-18 19:28, William Ray Wing wrote:
>
>> On Jul 18, 2015, at 1:34 PM, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
>>
>>
>
> [byte]
>
>> What is an {HP calculator} roll operation?
>>
>
> The original Hewlett Packard “Scientific” calculators (HP-35, 45, 65, etc) that used Polish notation (operand, operand, operation; with no “=“ sign) had a stack.

FYI, Polish Notation is a prefix notation; the operation comes first.

What you're talking about is Reverse Polish Notation, where the
operation comes last.

 > That stack itself could be manipulated (e.g., interchange X and Y). 
One of the stack manipulation commands was “Roll” which moved the top 
entry into X and pushed remaining elements up one.  Later versions had 
both Roll-up and Roll-down, Roll-down moved the X entry to the top of 
the stack and dropped the other elements.
>
> Bill  (Who still uses an HP-45 emulator on his iPhone)
>