HP 39g Graphing Calculator - Manual (Page 166)

storing and recalling variables
You can store numbers or expressions from a previous input
or result into variables.
Numeric
Precision
To store a value
A number stored in a variable is always stored as a 12-digit
mantissa with a 3-digit exponent. Numeric precision in the
display, however, depends on the display mode (Standard,
Fixed, Scientific, Engineering, or Fraction). A displayed
number has only the precision that is displayed. If you copy it
from the HOME view display history, you obtain only the
precision displayed, not the full internal precision. On the
other hand, the variable Ans always contains the most recent
result to full precision.
On the command line,
enter the value or the
calculation for the result
you wish to store.
Press BM3
Enter a name for the
variable.
51-B
4. Press I ENTER |.
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11-2 Variables and memory management