Procedure Pop(Var Item:Data);

    This  returns  Item  from  the  stack.    The  last  item  pushed  is
    returned and the item  is  removed  from  the stack.  If the stack is
    empty and debug  information  is  on,  then  a  check  is made and an
    error is returned.   If  debug  information  is  off,  the  unit will
    behave unpredictably when popping an empty stack.