```Chapter 9
Using the calculator

Subjects covered...

Selecting the calculator
Entering numbers
Running total
Using built-in mathematical functions
Editing the screen
Assigning variables
User defined functions
Exiting from the calculator

The +3 can be used as a full function calculator.

To use the calculator, call up the opening menu and select the
'Calculator' option. (If you don't know how to select a menu option,
refer back to chapter 2.)

The calculator may be selected as soon as the +3 is switched on.
Alternatively, if you are working on a +3 BASIC program, you may
select the calculator by choosing the 'Exit' option from the edit menu
(which returns you to the opening menu), at which point you can select
the 'Calculator' option. Note that any BASIC program which was being
worked on (when you selected the calculator) will be remembered and
restored when you exit from the calculator and return to +3 BASIC.

When you have selected the 'Calculator' option, the screen will change
to...

+-------------------------------------------------------------+
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|    [_Calculator________________________________________]    |
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+-------------------------------------------------------------+

...and the +3's calculator is ready to accept your first entry. Type
in...

6+4

As soon as you press ENTER, the answer '10' will appear. (Note that
you don't key in '=' as you would on a conventional calculator.)

You will see that the cursor is positioned to the right of the answer,
which is a running total (like on a conventional calculator). This
means that you can simply type in the next operation to be carried out
on the running total (without having to type in a whole new
calculation). So, with the cursor still positioned to the right of the
'10' on the screen, type in...

/5

...and back comes the answer '2'. Now type in...

*PI

This produces the result '6.2831853' on the screen. The +3 has used
its built-in pi function - all you had to do was type in PI. This
applies to all the +3's mathematical functions. To demonstrate, type
in...

*ATN 60

...which gives the result '9.7648943'. You may also 'edit' the
contents of the screen. To demonstrate, move the cursor (using the
cursor left key) to the beginning of the line and then type in INT

INT 9.7648943

...and as soon as ENTER is pressed, back comes the answer '9'. This
also demonstrates that the +3 doesn't have to perform a calculation in
order to print the value of an expression. As another example, press
ENTER and type...

1E6

...and back will come the value of that expression. Notice that before
you typed in '1E6', you pressed ENTER on its own - this tells the +3
that you are about to start a new calculation.

One extremely useful feature of the +3's calculator is that it will
allow you to assign values to variables and then use them in
subsequent calculations. This is achieved by using the LET statement
(as you would in BASIC). To demonstrate, press ENTER and type in the
following...

LET x=10

(You must then press ENTER twice for the +3 to accept the variable
assignment.) Now verify that the variable 'x' is being used, by
typing...

x+90

...then...

+x*x

If you are using the calculator whilst working on a BASIC program,
then any variables used by the calculator should be chosen so that
they do not conflict with those used by the program itself.

BASIC keywords are not allowed to be used as variable names.

When you have finished using the calculator, press the EDIT key. The
screen will change to...

+-------------------------------------------------------------+
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|                      _________________                      |
|                     |_Options_________|                     |
|                     |//Calculator/////|                     |
|                     |  Exit           |                     |
|                     +-----------------+                     |
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|     ___________________________________________________     |
|    [_Calculator________________________________________]    |
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+-------------------------------------------------------------+

working on a +3 BASIC program before you started using the calculator,
then you may return to the program by selecting the '+3 BASIC' option.
(If you wish to continue using the calculator, then select the
'Calculator' option.)

Note that if you have set up any user defined functions (using the
'DEF FN' statement) whilst working on a BASIC program, you will be
able to invoke that function when using the calculator. To illustrate

9000 DEF FN c(n)=n*n*n

...which sets up the user defined function 'FN c(n)' which returns the
'cube' of n (the number you type into the brackets). Now exit from +3
BASIC and return to the calculator - you can now use this user defined
function as if it were one of the +3's own built-in functions. For
example, enter...

FN c(3)

...and the calculator will print the number '27' (i.e. the cube of 3).

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