- STORAGE REGISTER OPERATIONS  
STORAGE REGISTER OPERATIONS

When numbers are stored or recalled, they are copied between the display(X-register) and the data storage registers. At "power-up" (initial turn-on) the HP-15C has 21 directly accessible storage registers: R0 through R9, R.0 through R.9, and the Index register(RI). Six registers, R2 to R7, are also used for statistics calculations.

The number of available data storage registers can be increased or decreased. The DIM function, which is used to reallocate registers in calculator memory, is discussed in "Memory Allocation".

Storing and Recalling Numbers

STO (store). When followed by a storage register address(0 through 9 or .0 through .9*), this function copies a number from the display(X-register) into the specified data storage register. It will replace any existing contents of that register.

RCL (recall). Similarly, you can recall data from a particular register into the display by pressing RCL followed by the register address. This brings a copy of the desired data into the display; the contents of the storage register remain unaltered.

x>< (X exchange). Followed by 0 through .9,* this function exchanges the contents of the X-register and the addresed data storage register. This is useful to view storage registers without disturbing the stack.

The above are stack lift-enabling operations, so the number remaining in the X-register can be used for subsequent calculations. If you address a nonexistant register, the display will show "Error 3".

Example: Springtime is coming and you want to keep track of 24 crocuses planted in your garden. Store the number of crocuses blooming the first day, and add to this the number of new blooms the second day.

Keystrokes          Display
3 STO 0            3.0000

Stores the number of first day blooms in R0.

Trun the calculator off. Next day, turn it back on again.

RCL 0              3.0000

Recalls the number of crocuses that bloomed yesterday.

5 +                8.0000

Adds today's new blooms to get the total blooming crocuses.

Storage and Recall Arithmetic

Storage Arithmetic. Suppose you not only wanted to staore a number, but perform arithmetic with it and store the result in the same register. You can do this directly-without using RCL-by using the following procedure:

1. Have your second operand(besides the one in storage) in the display(as a result of a calculation, a recall, or keying in).

2. Press STO.

3. Press +, -, *, or ÷ .

4. Key in the register address(0 to 9, .0 to .9). (The Index register, discussed elsewhere*, can also be used.)

The new number in the register is determined as follows:

For storage arithmetic,

new        = old      { + }  number
contents     contents { - }  in
of           of       { * }  display
register     register { ÷ }

R0 r     T t          R0 r-x     T t
         Z z                     Z z
         Y y                     Y y
         X x                     X x

Keys:              STO - 0

Recall Arithmetic. Recall arithmetic allows you to perform arithmetic with the displayed value and a stored value without lifting the stack, that is, without losing any values from the Y-, Z-, and T- registers. The keytstorke sequence is the same as for the storage arithmetic using RCL in place of STO.

For recall arithmetic,

new        = old      { + }  number
contents     contents { - }  in
of           of       { * }  display
register     register { ÷ }

R0 r     T t          R0 r       T t
         Z z                     Z z
         Y y                     Y y
         X x                     X x-r

Keys:              RCL - 0

Example: Keep a running count of your newly bloomong crocuses for two more days.

Keystrokes          Display
8 STO 0            8.0000

Places the total number of blooms as of day 2 in R0.

4 STO + 0         4.0000

Day 3: adds four new blooms to those already blooming.

3 STO + 0         3.0000

Day 4: adds three new blooms.

24 RCL - 0       9.0000

Subtracts total number of blooms summed in R0(15) from the total number of plants(24): 9 crocuses have not bloomed.

RCL 0              15.0000    (The number in R0 does not change.)