═══ 1. Introduction ═══

E-Teller Calculator is a simple calculator which is not dissimilar to the 
average (cheap) calculator one would generally find at one's local department 
store.  It does, however, have some features one would generally not find in 
the average (cheap) calculator. 


═══ 2. Using the Calculator ═══

To use E-Teller Calculator, press the appropriate numeric key.  As each numeric 
key is pressed, its corresponding number will appear in the display area of the 
calculator.  Press one of the operators (+ - / *) to perform the desired 
calculation. 

As each calculation takes place, the digits and operator will be appended to 
the end of the calculation tape at the bottom of the calculator window; for 
example: 

    1 + 2 = 3
    2 * 3 = 6

For additional help on the calculator keys, see the Calculator keys topic. 


═══ 2.1. Calculator keys ═══

This section describes some of the less apparent key functions and possible 
corresponding keyboard equivalents. 

Off (pushbutton) or O (keyboard) 
          turns the calculator off (effectively closing the application). 

Backspace 
          removes the right-most number from the display area. 

% 
          simulates a click on the % button. 

Clr (pushbutton) or Esc or C (keyboard) 
          clears the display area when it is first clicked (at which point the 
          background colour turns bright red).  When clicked a second time 
          (when the colour is bright red rather than dark red), the calculation 
          buffer is cleared and the button background colour returns to dark 
          red. 

M (pushbutton) or M (keyboard) 
          alone does nothing.  If a display number has been saved in the 
          calculator's memory (either by clicking on the M+ or M- buttons), 
          then the pushbutton caption will read M/r and an 'M' will appear in 
          the upper left-hand corner of the display.  Clicking the M/r button 
          places the saved number into the display area and changes the M/r 
          caption of the pushbutton to M/c.  Clicking the button at this stage 
          clears the calculator memory and removes the 'M' from the display 
          area. 

M- (pushbutton) or Alt+M 
          subtracts the amount in the display from the calculator memory or 
          adds a negative value if the memory is empty.  It also changes the M 
          caption from 'M' to 'M/r' as described above. 

M+ (pushbutton) or Ctrl+M 
          adds the amount in the display to value in the calculator's memory or 
          places the number in the display into the calculator's memory. It 
          also changes the M caption from 'M' to 'M/r' as described above. 

 and  (pushbutton) or Alt+Down and Alt+Up 
          respectively displays or hides the calculator tape and its 
          corresponding push buttons.  When the tape is hidden, calculations 
          are not appended to it. 

Clear (tape section) 
          erases the contents of the calculator tape. 

Delete (tape section) 
          deletes the selected items from the calculator tape. 

Print (tape section) 
          sends the contents of the calculator tape to the default printer. 

Stamp (tape section) 
          appends a date and time stamp to the calculator tape, for example: 

                         1 - 2 = -1
                         3 September 1994 (7:23pm)

          The date format is system dependent, whereas the time stamp is not. 


═══ 3. Notes ═══

When the calculator is turned off, the contents of the memory buffer, display, 
and calculator tape are saved to the etcalc.ini file, in addition to the 
location of the window and the visibility of the calculator tape section. 
These are restored when the calculator is next invoked. 

E-Teller Calculator traps syntax errors and displays the message Error - <error 
message> where <error message> is the error reported by Rexx in the display. 
These will generally be cryptic and of little use.  If you consistently get 
this sort of message, I would appreciate hearing about it.  Particularly useful 
would be a somewhat detailed description of what you did in order to get the 
error message.  The main purpose for trapping the errors is to avoid the 
calculator from closing unceremoniously. 

There is one error which E-Teller Calculator traps on its own.  Dividing an 
integer by zero is, of course, forbidden, and whenever a user inaverdently 
attempts such a calculation, the error message, Error - divide by zero, is 
displayed in the calculator's display area. 

Note:  In all cases, it would probably be a good idea to click on the Clr 
button twice in order to clear the calculation buffer.