PICK

Member Of Menu: 
Stack
Argument Types: 
Any
Real
Result Type(s): 
Any
Invertible: 
No
Valid In Expression: 
No
Stack Diagram: 
Item1 Item2 ... Itemn-1 Itemn Realn+1 → Item1 Item2 ... Itemn-1 Itemn Item1

This operation takes a real number which references an item on the stack. After popping that real number off of the stack, it uses that value as an index and copies that item off of the stack (1 is the top of the stack, 2 is the next item, etc). Finally, that copied item is pushed onto the top of the stack.