Calculators Why is My HP RPN Operation Displaying Unexpected Results?

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The discussion revolves around an unexpected behavior in the RPN (Reverse Polish Notation) operation of HP calculators. When a sequence of entries is performed—starting with the number 5, duplicating it in the stack, and then rotating the stack—the expected outcome after multiplying by 10 is that the stack would read (50, 5, 5, 0). However, the actual result is (50, 5, 5, 5), indicating that the T register retains its previous value instead of being zeroed out. This behavior is confirmed as correct, highlighting that the T register does not reset to zero after operations, which can lead to confusion for users expecting standard behavior. Further examples demonstrate that the calculator maintains values in the T register during operations, affecting subsequent calculations.
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HP strange RPN operation?

I just find an odd behavior on my hp rpn operation. Can someone try the following sequence of entry and explain to me this strange behavior?

Press 5 (any number will do).
Press 'Enter' (this should duplicate 5 to x an y stacks)
Press 'Enter' again (duplicate 5 again so now x,y and z stack are all 5)
Press 'RDn' to rotate stack 4 times (this should bring the stack configuration back to the same, x,y and z stack are all 5. The stack should read (5,5,5,0) for (x,y,z,t).
Now press 10 and then *.

Normally, I would expect the stack to be (50, 5, 5, 0) for (X, Y, Z, T). But if you follow the above step, you will get (50, 5, 5 ,5). Am I missing something here?
 
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That is the correct behavior. The T register is not zeroed, but remains the same. If you press 2 / enter / enter / enter, then press + many times, you will get 2, 4, 6, 8, 10, 12, 14, 16...
 

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