HP HP-67

58 The Automatic Memory Stack
The Key
When you key a number into the calculator, its contents are written
into the displayed X-register. For example, if you key in the number
314.32 now, you can see that the display contents are altered.
When you key in 314.32 with the stack contents intact from previous
examples the contents of the stack registers are changed...
...from this... ...to this.
T 4.00 T 4.00
Z 3.00 Z 3.00
Y 1.00 Y 1.00
X [0.00 Display. X 314.32| Display.
In order to key in another number at this point, you must first
terminate digit entry—i.e., you must indicate to the calculator that
you have completed keying in the first number and that any new
digits you key in are part of a new number.
Use the key to separate the digits of the first number from the
digits of the second.
When you press the key, the contents of the stack registers
are changed...
...from this... ...to this.
T 4.00 T 3.00
z 3.00 Z 1.00
Y 1.00 Y 314.32
X |314.32 Display. X |314.32 Display.
As you can see, the number in the displayed X-register is copied
into Y. The numbers in Y and Z have also been transferred to Z
and T, respectively, and the number in T has been lost off the top of
the stack.