# Rdx. And Rdx, Functions; Modes Menu; The Stack - HP -42S Manual

An alternative: hp-42s calculator and free42 simulator for palmos.

mode while 1000 will be 1.00E3 in the same mode. Why do we get 100.E0 for 100 instead of
100.00E2 in ENG 2 mode? Because the calculator shows in engineering mode the same number of
digits it shows in scientific mode.

## 2.6.5 RDX. And RDX, functions

In some countries like Brazil we use ',' for the decimal point instead of '.' and also '.' instead of ',' for
thousands separators. For example π is written here (Brazil) as 3,141 etc and not as 3.141 etc. In FIX
3 mode one million is written here as 1.000.000,000 and not as 1,000,000.000 as in English use. By
pressing RDX, you make the calculator to use ',' for the decimal point and by pressing RDX. we make
it use '.' for decimal point. Again the active mode is followed by a ■ sign. Here, in this manual, I
assume the calculator is using '.' for decimal point.

To access MODES menu just press
DEG actives degree mode for trigonometric functions. In this mode a circumference has 360°. RAD
actives radian mode and in this mode a circumference has 2π radians or just 2π.GRAD is not so
useful and correspond to 400 degrains for a circumference. For example: In degrees we have
sin(90°)=1 and in radians we have sin(π/2)=1.
Try this:
π
2 / COS in radians mode. Why the result is not exactly zero?
Answer: Because the number that calculator entered was not exactly π but 3.14159265359.
REC actives rectangular mode (x,y) and POLAR actives polar mode (r,θ). We will see this more in
detail when study complex numbers.
The MODES menu has another line but we will discuss this later. We will discuss the others menus
later too.

### 2.8 The Stack

The stack is intimately related to the way the calculator uses RPN to perform calculations so it's a
good idea to understand the concept and behavior of the stack. On the HP42S, the stack consists of 4
registers named X, y, z and t, and normally the values of x and y (or just x if a menu is active) are
displayed.
No calculator can store an infinite amount of data. In algebraic calculators the "( )" are limited to a
given number depending on the model. The same happens in RPN calculators. In some models like
HP-48 or HP-49 the amount of input data is limited only by available memory. But in other models
like 32SII, 33S (in RPN mode) and 42S the input data have to fit in a "stack" of four lines. There are
four lines labeled x, y, z and t. So the stack is something like
t: 0.0000
z: 0.0000
y: 0.0000
x: 0.0000
But since the calculator's display has only two lines just x and y lines are visible. When you enter a
number (say 2 ENTER) what happens is the following.
i) The content of lines t and z are lost.
ii) The content of line y goes to line t.
iii)The content of line x goes to line z.
iv)The content just entered goes to line y and line x.
MODES. (MODES is above +/– key).  