The xfunction is used primarily to swap the order of numbers in a calculation. For example, an easy way to calculate 9 ⎟ (13x8) is to press 13 E8 *9 x/.

Arithmetic－How the Stack Does It

The contents of the stack move up and down automatically as new numbers enter the X-register (lifting the stack), and as operators combine two numbers to produce one new number in the X-register (dropping the stack). See how a full stack drops, lifts, and drops its contents while calculating

 

 

 

3 ＋ 4 － 9 ：

 

 

 

 

 

 

 

 

 

a (lost)

T

 

 

 

 

 

 

 

 

 

a

 

a

 

a

 

a

Z

 

 

 

 

 

 

 

 

 

b

 

a

 

b

 

a

Y

3

 

 

 

 

 

 

 

3

 

b

 

7

 

b

X

E

 

 

 

 

 

 

 

4

+

7

9

9

-

－2

4

 

 

 

 

Drop

Lift

 

Drop

(a and b represent values already on the stack.)

„Notice that when the stack drops, it replicates the contents of the T-register and overwrites the X-register.

„When the stack lifts, it pushes the top contents out of the T-register, and that number is lost. This shows that the stack’s memory is limited to four numbers for calculations.

„Because of the automatic movement of the stack, you do not need to clear the display before doing a new calculation.

„Most functions (except Eand C) prepare the stack to lift its contents when the next number enters the X-register.

270 E: RPN: The Stack

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