Step 1. Open Arithmetic, make sure Stacks and Registers are visible.
When you first start HP Calc you should come up in the Arithmetic function. If not, press (MENU) Arithmetic on the HP 95LX or (MENU) Applications Arithmetic on the HP 100/200LX. The Registers and Stacks should be displayed. If they are not, press (F2) (SHOW) on the 95LX. On the HP 100/ 200LX press (MENU) Options Calculator Modes, make sure the "Show Stack and Show Registers boxes are checked and press (F10) (OK).
You should see a display that looks something like this:
Show Registers and Stack in HP Calc: Graphic
Step 2. Key in the number 4 and press (ENTER).
This enters 4 in the calculation line at the bottom right of the screen. Now we're ready to see what those keys do.
Step 3. Press the Z through M keys, see what happens.
Press the keys one at a time and watch what happens to the calc line and the Stack immediately above it. The Stacks are used to keep track of the last three numbers entered, a handy feature for some calculations.
If I key in 3.1, press (ENTER) and then key in 2.2 and press (ENTER), 3.1 is bumped up to the Stack 1 position (i.e. it is stored in Stack 1 buffer memory). If I then key in the number 5 and press (ENTER), 3.1 is bumped up to the Stack 2 position and 2.2 is bumped up to the Stack 1 position. If all three Stack positions have numbers in them and I key in a fourth number, the Stack 1 number is bumped to Stack 2, the Stack 2 number is bumped to Stack 3, and the Stack 3 number is bumped out of the Stack and forgotten by HP Calc.
The Registers can be used to store and recall additional numbers as described below. Below is a summary of what to expect.
Key pressed \ What happens (answer in example)
Z \ Calculates square root of number on Calc Line (2)
X \ Calculates the reciprocal the of number on Calc Line (0.50)
C \ Swaps the number on Calc Line with the number in Stack 1 position (0.00 if your stack was cleared).
V \ Moves Stack down one position. Stack 3 number moves to Stack 2, Stack 2 number to Stack 1, Stack 1 number to Calc Line, Calc Line number to Stack 3. (Calc Line = 0.50)
B (LAST) \ Copies number in Stack 1 to Calc Line. (Calc Line = 0.00. If you were in the middle of a calculation, say 1+2+, and pressed B, the number in Stack 1 would be copied into the calculation, 1+2+0.50. If you then pressed (ENTER), the answer, 3.50 would appear on the Calc Line.)
N (STO) \ Lets you STORE the number on the Calc Line in one of the Registers so you can access it later. (Key the number 1.4 into the Calc Line. Now press N (STO) and 0. Look up at the top of the screen to see that 1.4 is now stored in the Reg0 position.)
M (RCL) \ Lets you RECALL a number stored in the Registers. (Press 0 (ENTER) to clear the Calc Line. Now press M (RCL) 0 and 1.4, the number stored in Reg0, is restored to the Calc Line. You can use this feature in the middle of a calculation. So if you wanted to add the number in Register 0 to 5.2, you would press 5.2+ M0 and then press (ENTER).)
Although this example shows how the "Z" thorough "M" keys can
be used in the Arithmetic function, remember that they can be used in the
other HP CALC applications.