HP35s simple query about stacks

[Jeff O.]

Others will probably chime in with better explanations, but short and simple, you have discovered the replicating T-register behavior of the classic HP 4-level stack. Effectively, whenever you perform an operation on two values in X and Y, those values are consumed by your function and the result placed in X. The value initially in Z drops to Y, the value in T is copied to Z, but a copy also remains in T. If T had a zero, it appears that the stack is just dropping, but you can look at it as if the zero is being copied.