HP HP-21 - Controlling the Display; Display Key

Controlling the Display
In the HP-21, numbers in the display normally appear rounded
to only two decimal places. For example, the fixed constant 7,
which is actually used in the calculator as 3.141592654, nor-
mally appears in the display as (unless you tell the
calculator to show you the number rounded to a greater or
lesser number of decimal places).
Although a number is normally shown to only two decimal
places, the HP-21 always computes internally using 10 digits of
each number. For example, when you compute 2 X 3, you see
the answer to only two decimal places:
Press Display
2 I 3 3
However, inside the calculator all numbers have 10 digits. So
the calculator actually calculates using full 10-digit numbers:
2.000000000 3.000000000 [x]
yields an answer that is actually carried to 10 digits:
6.000000000
———
You see only
these digits. . . but these digits
are also present.
Display Key
The [osP] (display) key allows you to control only the manner
in which a number is displayed. The number itself is not altered
by the key.
Using the key, you can choose either of two ways to display
a number; fixed decimal point notation or scientific notation.
No matter what notation you choose, these rounding options
affect the display only—the HP-21 always calculates internally
with the entire number.
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