Question about Stack and Roll

[striegel]

wojtek, I think you misunderstand that Antlab said the '1' was missing from the stack.

(07-01-2016 03:16 PM)wojtek Wrote:  

(07-01-2016 02:03 PM)Antlab Wrote:  ... the registers are filled with the sequence:
T: 2.0000
Z: 3.0000
Y: 3.0000
X: 4.0000

This surprises me, because I was expecting the sequence 1, 2, 3, 4.
Probably I am missing some subtlety of the RPN Roll behaviuor, could you please help me to understand what happens?
Thanks.

It is correct (if you press Roll Down after each Enter). I believe all HP rpn calculators behave the same way. Make a quick test and clear the stack (press "clear" and Enter 4 times) then press: 1, Enter , 2. You will get the stack with: 0,0,1,2 (from T to X). But if you press Enter after 2 as well and then will inspect the stack it will contain: 0,1,2,2 (withs X register duplicated in Y). This is because of convention applied by HP that Enter moves up the stack and sets some flag what makes the next number entered replace the duplicated X register. If you press Roll down the flag is cleared and the duplicated value remains in X and Y registers