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Stack-Up happened in 1985.
Stack-Up was created on 1985-07-26.
The answer depends on what the stack is made up of.
Click on the stack to pick the whole stack up, then right click on an empty inventory slot to deposit a single unit of the stack.
If your stack grows bottom-up, it's decremented when you leave a function; if the stack grows top-down, the stack pointer is incremented.