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,

πis always represented internally as 3.141592654×1000, 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 ukey 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 π 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.