HP 15c - Manual (Page 22)

22 Section 1: Getting Started
Calculations
One-Number Functions
A one-number function performs an operation using only the number in the
display. To use any one-number function, press the function key after the
number has been placed in the display.
Keystrokes Display
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Two-Number Functions and
v
A two-number function must have two numbers present in the calculator
before executing the function. +, -, * and ÷ are examples of
two-number functions.
Terminating Digit Entry. When keying in two numbers to perform an
operation, the calculator needs a signal that digit entry is terminated for the
first number. This is done by pressing v to separate the two numbers.
If, on the other hand, one of the numbers is already in the calculator as the
result of a previous operation, you do not need to use the v key. All
functions except the digit entry keys themselves
*
have the effect of
terminating digit entry.
Notice that, regardless of the number, a decimal point always appears and a
set number of decimal places are displayed when you terminate digit entry
(as by pressing v).
Chain Calculations. In the following calculations, notice that:
 The v key is used only for separating the sequential entry of
two numbers.

The operator is keyed in only after both operands are in the calculator.

The result of any operation may itself become an operand. Such
intermediate results are stored and retrieved on a last-in, first-out
basis. New digits keyed in following an operation are treated as a new
number.
*
The digit keys, +, “, ‛, and −.