HP -10C Owner's Handbook Manual page 17

The v Key. If one of the numbers you need for a two-number function is
already in the calculator as the result of a previous operation, you do not need to
use the v key. However, when you must key in two numbers before
performing a function, use the v key to separate the two numbers.
To place two numbers into the calculator and perform a two number function
such as 2 ÷ 3:
1. Key in the first number.
2. Press v to separate the first number from the second.
3. Key in the second number.
4. Press the function key(s).
Keystrokes
2
v
3
÷
Now try this problem. Notice that you have to press v to separate
numbers only when they are being keyed in one immediately after the other. A
previously calculated result (intermediate result) will be automatically separated
from a new number you key in.
To solve (9 + 17 − 4 + 23) ÷ 4:
Keystrokes
9v
17+
4-
23+
4÷
Even more complicated problems are solved in the same simple manner—using
automatic storage of intermediate results. (For problems with nested
parentheses, refer to Chain Calculations, page 24.)
Example: Solve (6 + 7) × (9 − 3).
First solve for the intermediate result of (6 + 7):
Keystrokes
6
v
7
Display
2.
2.0000
3.
0.6667
Display
9.0000
26.0000
22.0000
45.0000
11.2500
Display
6.
6.0000
7.
Section 1: Getting Started
(9 + 17).
(9 + 17 − 4).
(9 + 17 − 4 + 23).
(9 + 17 − 4 + 23) ÷ 4.
15