HP 50g User Manual page 816

The keystrokes necessary for entering these values in Algebraic mode are the
following:
...¹2` R5`
The same calculations can be produced in RPN mode. Stack levels 3: and 4:
show the case of Exact CAS setting (i.e., the _Numeric CAS option is
unselected), while stack levels 1: and 2: show the case in which the Numeric
CAS option is selected.
The required keystrokes are: 2...¹ 5R
A keyboard short cut to toggle between APPROX and EXACT mode is by
holding the right-shift key and pressing the ENTER key simultaneously, i.e.,
‚ (hold) `.
Real numbers vs. integer numbers
CAS operations utilize integer numbers in order to keep full precision in the
calculations. Real numbers are stored in the form of a mantissa and an
exponent, and have limited precision. In APPROX mode, however, whenever
you enter an integer number, it is automatically transformed into a real number,
as illustrated next:
Whenever the calculator lists an integer value followed by a decimal dot, it is
indicating that the integer number has been converted to a real representation.
This will indicate that the number was entered while the CAS was set to
APPROX mode.
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