HP 15c - Manual (Page 60)

60 Section 5: The Display and Continuous Memory
Mantissa Display
Regardless of the display format, the HP-15C always internally holds each
number as a 10-digit mantissa and a two-digit exponent of 10. For example,
π is always represented internally as 3.141592654×10
00
, regardless of what
is in the display.
When you want to view the full 10-digit mantissa of a number in the X-
register, press ´ CLEAR u. To keep the mantissa in the display,
hold the u
key down.
Keystrokes Display
| $ 3.1416
´ CLEAR
u (hold)
3141592654
Round-Off Error
As mentioned earlier, the HP-15C holds every value to 10 digits internally.
It also rounds the final result of every calculation to the 10th digit. Because
the calculator can provide only a finite approximation for numbers such as

or 2/3 (0.666…), a small error due to rounding can occur. This error can be
increased in lengthy calculations, but usually is insignificant. To accurately
assess this effect for a given calculation requires numerical analysis beyond
our scope and space here! Refer to the HP-15C Advanced Functions
Handbook for a more detailed discussion.
Special Displays
Annunciators
The HP-15C display contains eight annunciators that indicate the status of
the calculator for various operations. The meaning and use of these
annunciators is discussed on the following pages:
* Low-power indication, page 62.
USER User mode, pages 79 and 144.
f and g Prefixes for alternate functions, pages 18-19.
RAD and GRAD Trigonometric modes, page 26.
C Complex mode, page 121.
PRGM Program mode, page 66.