The X and Y–Registers are in the Display

The X and Y–Registers are what you see except when a menu, a message, an equation line ,or a program line is being displayed. You might have noticed that several function names include an x or y.

This is no coincidence: these letters refer to the X– and Y–registers. For example,

raises ten to the power of the number in the X–register.

Clearing the X–Register

Pressing () always clears the X–register to zero; it is also used to program this instruction. The key, in contrast, is context–sensitive. It either clears or cancels the current display, depending on the situation: it acts like

1() only when the X–register is displayed. also acts like () when the X–register is displayed and digit entry is terminated (no cursor present).

Reviewing the Stack

R (Roll Down)

The (roll down) key lets you review the entire contents of the stack by "rolling" the contents downward, one register at a time. You can see the numbers as they roll through the x- and y-registers.

Suppose the stack is filled with 1, 2, 3, 4. (press ) Pressing four times rolls the numbers all the way around and back to where they started:

T

1

 

4

 

3

 

2

 

1

Z

2

 

1

 

4

 

3

 

2

Y

3

 

2

 

1

 

4

 

3

X

4

 

3

 

2

 

1

 

4