Big Blue Disk 43/bbd43.zip/PCSTART.TXT

Text File | 1990-03-19 | 33KB | 648 lines

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^Cby
^CDoug Harrison

 Getting Started
 ---------------
 Welcome to Personal Calc (PC), Big Blue Disk's spreadsheet program for the IBM
 PC and compatibles.  A spreadsheet program makes working with rows and columns
 of numbers easier.  Spreadsheets (also called worksheets) are designed to look
 like the forms accountants use for bookkeeping.

 One common example of a paper spreadsheet is the typical timesheet you may
 have used as an employee.  On the left column of the page, the timesheet might
 have several budgets to which your time is charged.  Across the top, the
 timesheet could have the days of the week.  You enter your hours in the box
 where the row (budget) and column (day) meet (called a cell).  On the right
 you might sum the hours for each budget, and at the bottom, you could sum the
 hours for each day.  At the bottom left would be the total hours for that
 week.

 The central feature of the spreadsheet is the cell grid, arranged in rows and
 columns, where each cell has a unique address or name.  Cells may contain
 numbers, text or formulas (the latter are algebraic expressions that may refer
 to other cells, allowing you to create complex models).

 Spreadsheet programs make working with numbers much easier, because they can
 calculate complex formulas automatically.  One of the most important features
 of a computer spreadsheet, however, is that it allows you to change the data,
 automatically recalculating the worksheet for you.  This has made it possible
 to analyze financial and other numeric information more easily and creatively
 than was normal before electronic spreadsheets.

 Running PC
 ----------
 To start Personal Calc, type PC at the DOS prompt.  If you wish PC to load a
 file right away, invoke it with the command PC filename, where filename has
 the form [optional path]name.ext.  The filename extension must be PCW
 (Personal Calc's own format); WKS, and WK1 (Lotus 123 Release 1 and 2 format)
 files may also be imported into Personal Calc, usually with no loss of
 information.

 If your video adapter displays "snow," specify the command line switch /s,
 which informs PC to update the screen more slowly to avoid the snow.  The full
 specification for the PC command line, therefore, is:

 pc [/s] [filename]

 where the brackets indicate optional items.

 Personal Calc looks for several support files as it loads.  These are:

     PRINTER.INF (contains printer control codes),
     PC.CFG (general configuration information), and
     PC.HLP (help file).

 In order for PC to find these files, they must be in the same subdirectory as
 PC.EXE, and the subdirectory should also be the current DOS path.  If PC is
 unable to find these files, it will display a message and continue loading.

 A Quick Look at PC
 ------------------
 At the DOS prompt, type

 CD \PERSCALC
 PC

 (Type "CD" plus the name of the subdirectory containing Personal Calc, and
 press Enter after each line.)  At the Personal Calc title screen, press Enter
 to enter the program.  Notice the words at the top of the screen.  These are
 part of the menu system described in detail below.  For now, press Alt-F
 (File) and the letter, O (Open) type EXAMPLE.PCW then press Enter.  On the
 screen you should see the budgeting spreadsheet included on the PC disk.

 Use the cursor keys to highlight the area in the column B and row 17 (this
 cell is called B17).  Just below the words File and Edit at the top left of
 the screen, you should see the cell number, B17.  This cell is beside the
 word, Rent, and below Amount Budgeted.  Type 550 and press enter.  Notice that
 the program supplied the dollar sign, and that the Difference column has
 calculated a number, $550.  Cursor right once to cell C17 and type 500 and
 Enter.  Cell D17 has changed again, this time to $50.  Cursor right to cell
 D17 and look at the second line of the computer monitor: it should show that
 you are in cell D17, and that the formula in that cell is =B17-C17.  Cursor to
 B18 and enter 100, then enter 125 in B19.  The Electric Utility Difference,
 calculated in cell D18 is a negative number: ($25).

 Now, cursor to cell A16 and press Ctrl-T B Enter (Freeze Titles Both is the
 name of the command you just executed).  The cursor moved down and to the
 right one cell, and now you will be unable to cursor up or to the left.
 That's good, and to see why, cursor down until you see row 57 in the lower
 left of your screen.  Notice that the titles on the upper part of the screen
 remain frozen so we will know what column we are in.

 Look at the figures on row 57.  They show that between our two budget items
 entered so far, $650 has been budgeted and $625 has been spent, leaving a $25
 cash reserve.

 Press Ctrl-Home to get to the top left of the active cell area (cell B17).  To
 unfreeze the titles press Ctrl-T B U (Freeze Titles Both Unfreeze).  Ctrl-Home
 will take you to A1 this time.

 Cursor to A11 and press the F2 function key.  On the second line of the
 screen, below the word, Format, you will see the contents of cell A11.  Press
 the End key, and the cursor will move to the end of this data.  Use Backspace
 to erase the underline characters and enter your name after the "Name:"
 prompt.  Press Enter to keep the change, then type the date into cell D11
 using the same technique.

 Now we'll quit our quick trip into PC, but we'll save our work under a new
 name so you can come back to it later.  Press Alt-F A (for File Save As), type
 a new name (SCRATCH, for example) and press Enter.  To quit, press Alt-F Q or
 just Ctrl-Q.  While this only scratches the surface of what PC can do, it
 shows how easy it is to put a spreadsheet to work doing those tedious math
 chores.

 Personal Calc Basics
 --------------------
 The PC screen is broken down into several areas.  The menu bar is at the top
 of the screen; it consists of several menu commands, which are selected by
 holding down the Alt key while tapping the highlighted key (for example, Alt-E
 brings up the Edit menu).

 Directly underneath the menu bar, to the left of the vertical line, is the
 cell reference bar.  It contains the current cell address or location of the
 cell pointer, which will be in cell A1 (as long as you did not load a file
 when you launched PC.)

 Directly to the right of the cell reference bar is the formula bar.  You enter
 data into cells by typing it in the formula bar, which functions as a tiny
 text editor.

 Below the cell reference and formula bars is the cell grid.  Columns are
 identified by letters and rows by numbers.  PC provides 255 columns; columns
 1-26 are specified with the letters A-Z, columns 27-52 by AA-AZ, columns 53-78
 by BA-BZ, and so on through column 255, IU.  PC provides 999 rows, numbered 1-
 999.  A cell address consists of the column name followed by the row number,
 as in A1, Z456, and CD222.

 The status bar is beneath the cell grid.

 Working with the Menu Bar
 -------------------------
 To activate a menu title and drop down the associated menu, press Alt plus the
 menu title hot key (which is either underlined or in a distinctive color on
 the screen).  For example, to access the File menu, press Alt-F.  The menu
 title becomes highlighted, and the file operations menu appears directly
 beneath it.  Within the menu are various items, such as New, Save, Print, and
 so forth.  The highlight bar indicates the item which will be selected should
 you terminate the menu by pressing Enter.  You may move the highlight bar by
 pressing the up and down arrow keys or Home/End.  You may cancel the menu by
 pressing Esc.  Should you pull down one menu but instead need to access
 another, you can activate adjacent menu titles by pressing the left/right
 arrow keys.

 PC follows several conventions when it displays menu items.  Those followed by
 ellipsis (...) invoke a dialog box, which asks for or displays further
 information.  Menu items followed by a triangle symbol have an associated sub-
 menu, which will appear to the right of the parent menu when the item is
 selected.  Sub-menus behave just like parent menus; you may cancel a sub-menu
 with Esc and return to the parent menu.  Menu items followed by a caret (^^)
 and a letter or number designate hot keys; you may bypass the menus and invoke
 the function directly, by pressing Ctrl plus the hot key.  Function key hot
 keys are listed as F1, F2, and so on.  Finally, some menu items function as
 on-off switches; the on state is indicated by a diamond preceding the menu
 item, while the off state is identified by lack of a diamond.

 Like the menu titles, notice that most menu items have hot key characters;
 while a menu is displayed, you can directly select a menu item, leaving the
 menu, by pressing the key by itself, since Alt is generally not required.

 Working with Dialog Boxes
 -------------------------
 Personal Calc uses dialog boxes to get information about functions it is to
 perform.  Dialog boxes contain the following items:  action buttons, displayed
 as text enclosed in a rectangle; on-off switches, which have the form "[ ]
 option"; radio buttons, which have the form "( ) option"; editable fields,
 displayed as an empty rectangle preceded by a text identifier; and scrollable
 lists, displayed as a vertical list of text items contained within a
 rectangle.

 A PC form always has an active object, which contains the blinking cursor.
 When an object is active, you may select or change it in some way.  With this
 in mind, let's take a closer look at the object types listed above.

 Action buttons

 These buttons may cause an exit from a form, in which case they will typically
 have names like "OK" or "Cancel" (the Esc key is a synonym for "Cancel" in all
 forms).  PC forms generally have a default exit button, which is surrounded by
 a double rectangle.  You may select this Default button and exit the form by
 pressing Enter, even if another object is the active one.  When an action
 button that is not also the Default button is the current active object, PC
 will remove the double rectangle from the default object and place it around
 the active object, which may be selected by pressing Enter.

 Another variant of the action button does not cause an exit from the form;
 rather, it invokes another form.  Typically, when the secondary form is
 exited, control returns to the first.

 On-off switches

 When in the on state, these buttons have an "X" between the leading brackets.
 When off, the brackets are empty.  To alternate between the two states, press
 Space.

 Radio buttons

 These buttons are named after old-fashioned car radio controls; only one
 button within a group may be selected at any time.  The selected radio button
 has a dot between the leading parentheses.  You may cycle the selected object
 through a group of radio buttons with the up/left and down/right arrow keys,
 wrapping around from the first to the last object in the group and vice versa.

 Editable fields

 This object type allows you to enter text into a form.  The keyboard command
 structure is identical to the spreadsheet Edit mode, which will be discussed
 under "Working with the Formula Bar."

 Scrollable lists

 Scrollable lists present you with a vertical list of text items, out of which
 you may select only one.  The active item will be highlighted, and it will
 also contain the blinking cursor.  Navigate the list with the up and down
 arrow keys, PageUp and PageDown keys, and Home and End keys.  Lists may
 contain more items than can be simultaneously displayed, so are scrollable.
 Such lists appear in the File Selector, Define Name, and Goto Cell dialog
 boxes.

 Activating objects

 PC forms are generally ordered so that Tab activates the next object, and
 Shift-Tab activates the previous object.  Many objects have an associated hot
 key, like the menus.  If the current active object is not an editable field,
 you may simply press the relevant hot key; otherwise, you must press Alt and
 the hot key.  Enter exits the dialog box, choosing the default item (or active
 exit button), and Esc cancels the form.

 The File Selector

 The PC file selector is a good example of a dialog box, and it provides a
 simple interface for entering DOS filenames and path information.  The current
 path is displayed in the path line; to move to a new directory, enter the
 scrollable list, which always displays the contents of the current directory.
 Sub-directories are preceded by a down-arrow symbol, while the parent
 directory is represented by the DOS "two dot" notation, prefaced with an up-
 arrow symbol.  To move into a given directory, highlight it and press Enter or
 Space.  If you exit a root directory, the File Selector presents a list of
 disk drive letters, enclosed in brackets.  You move to a new drive the same
 way. Of course, you may type the filename directly, bypassing use of the
 scrollable list.

 Working with the Formula Bar
 ----------------------------
 The formula bar provides a text editor for entering data into the active cell,
 which is highlighted by the cell pointer; its address is displayed in the cell
 reference bar (to the left of the formula bar).  To enter data into the active
 cell, activate the formula bar by typing characters.  To change the cell, you
 must press Enter.

 You may cancel an entry in one of two ways:  press Ctrl-Z, or press Esc twice.
 Pressing Esc once clears the formula bar but allows you to continue editing,
 while a second press of Esc cancels the entry.

 When the active cell contains data, and you type, the formula bar contents are
 replaced by the character you typed.  Unless you cancel the entry, the old
 information will be erased and replaced by the new.

 Enter and Edit Modes

 Activating the formula bar by typing automatically places you in Enter mode
 (note the Status Bar at the bottom of the screen).  Enter mode has minimal
 editing features and is handy for fast data entry, since you can lock in the
 entry and move the cell pointer by pressing the arrow keys (among others).

 If you need to edit an existing entry, activate the formula bar by pressing
 F2.  This places you in Edit mode (note the Status Bar), and a tiny text
 editor is available.  You may cancel entries just as in Enter mode, but the
 only way to lock in the entry is by pressing Enter, which does not move the
 cell pointer.  You may alternate between Enter and Edit modes by pressing F2.

 The table below summarizes the keyboard command structure for Enter and Edit
 modes.

 Keystroke         Action
 ---------         ------
 Enter             Lock in entry.  Does not move cell pointer.
 Esc               Once, clear formula bar; twice, cancel entry.
 Ctrl-Z            Cancel entry.

 Cursors           Enter mode, lock in entry and move cell pointer.
                   Edit mode, move text cursor in formula bar.

 Tab               In Enter mode, lock in entry and move cell
 Shift-Tab         pointer one screen right or left.

 PageUp/PageDown   In Enter mode, lock in entry and move cell
                   pointer one screen up or down.  In Edit mode,
                   move the text cursor one "formula bar's" worth
                   of data up or down.

 Shift+Arrow       Selects block of text in both modes.

 Ctrl-             Moves text cursor by words in both modes.
 Left/Right Arrow

 F2                Switch between Edit and Enter modes.

 The menu bar is inactive while you are working with the formula bar.

 Text Selections

 As described above, you may select blocks of text using Shift plus the arrow
 keys.  The text cursor will disappear, and the block will be highlighted.  To
 replace the block, just begin typing; the block will be deleted and the new
 text inserted in its place.  To cancel the selection, press one of the arrow
 keys.

 Working with the Cell Grid
 --------------------------
 Moving the Cell Pointer

 The cell pointer is the highlighted bar found in the active cell.  The arrow
 keys move the cell pointer one cell in the indicated direction.  PageUp and
 PageDown scroll the worksheet one screen up and down, respectively, moving the
 cell pointer in the process.  Tab and Shift-Tab scroll the worksheet one
 screen right and left, respectively, and they too move the cell pointer.  Home
 moves the cell pointer to the column A in the row containing the active cell,
 while End moves the cell pointer to the last occupied column in this row.
 Ctrl-Home moves the cell pointer to the upper left occupied cell in the
 worksheet, while Ctrl-End moves the cell pointer to the lower right occupied
 cell in the worksheet.

 Selecting Ranges

 Ranges are rectangular worksheet areas displayed in inverse video (while
 inside a range the cell pointer is displayed in normal video), which designate
 an area over which some function is to act.  You initiate a range selection by
 pressing Shift plus one of the cursor keys, PageUp, or PageDown.  To extend
 the range, you may release the Shift key and use the cursor keys, PageUp,
 PageDown, Tab, Shift-Tab, Home, and End.  You may also begin a selection or
 extend one by pressing Ctrl or Shift (or both) plus Space.  The table below
 summarizes the action of these keys, assuming the selection process has
 already begun.

 Keystroke               Action
 ---------               ------
 Arrow keys              Extend selection one column or row

 PageUp/PageDown         Extend one screen up or down

 Tab/Shift-Tab           Extend one screen right or left

 Home                    Extend to column A

 End                     Extend to last occupied column in current row

 Shift-Space             Extends selection over all columns (selects
                         involved rows completely)

 Ctrl-Space              Extends selection over all rows (selects
                         involved columns completely)

 Shift-Ctrl-Space        Extends selection to encompass the entire
                         worksheet

 As an example, if the range C4:E6 were already selected, to extend the
 selection so that rows 4-6 are completely selected, you would press Shift-
 Space.

 During the course of the selection, you will notice that the cell reference
 bar displays the size of the range as "aaa R x bbb C", so you can tell at a
 glance how many rows and columns are involved in the selection.  This is
 especially useful when selecting ranges for cut/copy and paste.

 To complete the selection press Enter; to cancel it at any time, press Esc.
 Should you try to edit a cell while a range is selected, it will become
 deselected.  Thus, it is best to select a range and immediately invoke the
 function requiring the range.

 Many functions require you to specify a range upon which they are to act.  As
 the menu bar is inactive during range selection, you will have to first
 complete the selection to access these functions.  However, the following hot
 keys both complete the selection and invoke the function:

 Keystroke   Action
 ---------   ------
 Ctrl-X      Edit Cut
 Ctrl-C      Edit Copy
 Ctrl-V      Edit Paste
 Ctrl-B      Edit Clear
 Ctrl-I      Edit Insert
 Ctrl-D      Edit Delete
 Ctrl-W      Column Width
 Ctrl-P      Precision

 Most functions assume that when no range is selected, the active cell
 constitutes a one-cell range.

 Selecting a range does not move the cell pointer; once the selection has been
 completed, PC returns the worksheet display to the area shown before the
 selection was begun, and the cell pointer returns to its original location.

 The Status Bar
 --------------
 The status bar appears at the bottom of the screen.  The left portion of the
 status bar always displays PC's current mode, including Ready, Enter, Select,
 Edit, Copy, and Cut, and so on.  The right side of the status bar displays
 active cell-specific information, including number format, hidden and
 protected status, and column width.

 Number format has the general form "xnn," where "x" is a letter corresponding
 to one of PC's 6 basic formatting styles and "nn" the precision.  The letters
 used are:  F for Fixed, S for Scientific, P for Percent, C for Currency,  O
 for Comma, and D for Date/Time.  The General format is a special case,
 represented by "Gen" since precision is irrelevant in that format.  Date/Time
 is also special in that the two digits are the number of the date/time format.

 When the active cell has text format, the justification (Lft, Ctr, or Rt) is
 displayed rather than a number format.

 The column width indicator has the form "Wxx," where xx is equal to the width
 of the column containing the active cell in characters.

 The hidden and protected cell indicators have the form "H" and "P"
 respectively.  They only appear when the active cell is hidden or protected.

 Between the mode indicator on the left and the active cell-specific indicators
 on the right are the Circular Reference and Recalculation indicators.  If
 natural order calculation is in effect, and a circular reference exists, the
 "Circ" indicator appears; it remains until the circular reference no longer
 exists or natural order is turned off.  The recalculation indicator, "Calc,"
 appears if a cell value is altered and Automatic calculation is not in effect;
 it indicates that the worksheet needs to be calculated, either by pressing F9
 or activating automatic calculation.

 Cell Classes
 ------------
 As mentioned earlier, spreadsheets typically support three cell classes:
 numeric, text, and formula.  PC chooses the format for you, based upon the
 following rules.

 Numbers begin with a digit, minus sign, or decimal point.  You may enter
 numbers in scientific notation, such as 1E3 (read "1 times 10 to the 3rd
 power").  Examples of acceptable numbers are:  1, .2, 3.4, -.5, and 1.234e-20.

 You may also enter numeric data using date/time notation.  For example,
 entering 1/1/90 would create a serial date value representing that date.
 Typing 13:45 would enter a time value representing 1:45 PM.  See Format
 Date/Time for directions on giving the cell a date or time format.

 The final way to enter a numeric value is by entering "NA".  This creates a
 numeric cell with the NA error status.

 Formulas begin with an equals or plus sign, followed by the formula.  As with
 the numeric class, PC checks the syntax of the formula.

 Text consists of entries that conform to neither the number or formula
 specifications noted above.  Text may use one of several special leading
 characters:  single quote indicates left justification, the caret (^)
 centering, and the double quote, right justification.  To enter the address,
 5455 Prytania, you would need to preface it with one of these three
 characters; otherwise, PC would interpret it as an invalid number.  PC does
 not display the text prefixes, but justifies the cell as indicated.  When you
 type normal text, you do not have to begin the text with one of these special
 symbols; PC will give such cells the default justification.

 If you enter a string beginning with the backslash (\), the character
 immediately following it is repeated to fill the cell completely.  For
 example, "\=" would completely fill the cell with equals signs, which is handy
 for creating dividers.

 Numbers in PC have the range 1E-308 to 1E308 or thereabouts, with 14 decimal
 digits of precision.  The maximum length of formulas and text entries is 240
 characters.

 Formulas
 --------
 PC formulas begin with the equals or plus sign, and they consist of algebraic
 expressions composed of operators, numbers, cell and range references, named
 cells and ranges, and functions.  Consult the function reference file for more
 information, but following is a brief introduction to formula notation.

 Cell/Range References

 You write a cell reference by combining the column name with the row number.
 Examples include A1, T240, and BA876.  Range references consist of two cell
 references separated by the colon, such as A1:B5, Z230:DA350.  Notice that the
 first cell in the range reference is the upper left cell in the range, while
 the second cell is the lower right cell in the range.  These are referred to
 as the range endpoints; PC will not permit you to reverse their order.

 Relative vs. Absolute Cell References

 A relative cell reference is written as described above.  Absolute cell
 references precede the column and/or row number with a dollar sign, as in $A1,
 A$1, and $A$1.  This notation may be used in range references as well.  This
 has no effect upon calculation, but it is significant when you copy or move
 cells.

 Operators

 PC supports the following operators, listed in order of decreasing precedence:

 -                 (unary minus or negation operator),
 * /               (multiplication and division),
 + -               (addition and subtraction),
 = <> > >= < <=    (Boolean or conditional operators).

 PC performs exponentiation via the POW function.

 Operators of equal precedence are listed on the same line, and they are
 evaluated left to right.  Parentheses may be used to force grouping in the
 standard way.

 A few simple (if meaningless!) examples should illustrate the above nicely.

 Ex.  1:  =1+2*3
 Evaluates to 7, as if it were 1+(2*3).  The precedence rules make the
 parentheses unnecessary.

 Ex.  2:  =-(-(3+5)*8)
 Evaluates to 64.  Here, parentheses are used to force grouping so
 that -8 is multiplied by 8.

 Ex.  3:  =1>=0.1*20
 Evaluates to 0.  This is a conditional expression, and the result of a
 conditional is either 1 (the condition is TRUE) or 0 (the condition is FALSE).
 1 >= 2 is clearly FALSE, so the result is 0.  Notice that the precedence rules
 again make parentheses unnecessary.

 Now, obviously there is no great advantage in using a spreadsheet to compute
 formulas like those above.  But things become much more interesting as we
 start to substitute cell references for numbers in formulas.  For example,
 suppose you entered five numbers in cells A1 through A5, and you wanted to
 total the numbers.  This formula would do the job:  =A1+A2+A3+A4+A5.  Now, you
 could enter a new value into A3, say, and PC would automatically recompute the
 formula.

 An easier way to accomplish this would be to use the SUM function; the formula
 would then be =SUM(A1:A5).  Note that the function argument is a range
 reference; you compose a range reference by typing the cell reference of the
 upper left cell in the range, a colon, and then the cell reference of the
 lower right cell in the range.

 Of course, you may use functions in formulas, just as you use numbers and cell
 references; for example, POW(SIN(A1),2)+POW(COS(A1),2) returns one for any
 number stored in A1.  PC provides a wealth of functions:  transcendental,
 financial, table lookup, date/time, and more.  .

 Error Status

 Formula cells may assume several error statuses, and PC displays a short error
 message in such cells.  For example, =1E200*1E200, causes a numeric overflow,
 as the result is 1E400, which is much greater than PC's maximum representable
 value of 1E308.  PC would display the "Overflow" message in a cell containing
 this formula.  Any cells referencing that cell would assume the Overflow
 status, too.  PC's other error messages are:  DivBy0, BadCellRef, OutOfRange,
 BadReal, Undefined, NA, and ERR.

 Calculation Modes
 -----------------
 Automatic Calculation

 If Automatic Calculation is in effect, PC calculates the entire worksheet
 whenever a cell value changes.  For example, if you enter a number into an
 empty cell, PC would calculate the worksheet.  Or, if you were to edit and
 change the value of an existing cell, PC would again calculate the worksheet.
 Copying cells, filling ranges, and inserting and deleting rows and columns,
 all force a recalculation.  When Automatic mode is not in effect, PC will
 calculate the worksheet only when you press the F9 key (of course, newly
 entered formulas are calculated, but the entire worksheet is not).

 Since PC calculates the entire worksheet when Automatic mode is in effect,
 entry of new cells may slow considerably as the worksheet grows.  Thus, for
 large worksheets, you will often want to disable Automatic calculation to
 avoid this delay.  When Automatic mode is disabled, and a cell value changes,
 PC will display the "Calc" indicator in the status bar to remind you to update
 the worksheet manually, either by pressing F9 or enabling Automatic mode.  You
 will also see the Calc indicator after sorting a range, even if Automatic mode
 is in effect.

 Other spreadsheets tend to calculate worksheets every time they are loaded
 from disk, whether they need to or not.  PC does not.  In fact, native PC
 files save the "Calc" status, which is restored when the program is loaded.

 Natural Order Calculation

 Whenever PC encounters a cell reference in a formula, it must retrieve the
 cell's value in order to use it.  But what if that referenced cell itself
 refers to another cell?  If that second cell has already been evaluated, then
 PC can simply use its current value and proceed in calculating the first.  If
 that second cell has not been evaluated, its value could change, and the
 current value would not be correct.  Thus it would be good to evaluate the
 formula before using the formula result.  If that second cell refers to a
 third, which also hasn't been evaluated, the problems mount.

 With the above discussion in mind, obviously PC should evaluate the third cell
 before using its value in the second.  This process of evaluating precedent
 cells before dependent cells continues until PC encounters a cell reference
 which refers to no other formula-type cells.  Its value can be computed and
 used in the cell that referenced it, and once that cell is fully evaluated,
 its value can be used in the cell that referenced it.  This process is called
 Natural Order calculation, since cells are calculated based upon the order in
 which they refer to other cells, rather than respective to their physical
 locations in the worksheet.  Hence, when Natural Order is enabled, PC assumes
 responsibility of determining the proper calculation order; you do not have to
 worry about the physical order of the cells in the worksheet.

 When Natural Order is off, PC calculates cells row by row.  That is, pressing
 F9 results in calculation of row 1, followed by row 2, and so on.

 Most of the time, you will want to use Natural Order, since calculation not
 only proceeds in a more intuitive way, it's much easier to construct worksheet
 models that do not depend on the physical order of the formulas.  However,
 Natural Order does present one complication:  circular references.

 Circular References

 A circular reference exists when one formula refers to a second that either
 directly, or indirectly (through a chain of cells), refers back to the first.
 When Natural Order is in effect, PC would begin evaluating the first cell and
 see that it refers to a second cell.  But when it tries to compute the second
 cell before using its value in the first, it discovers that the second cell
 refers back to the first.  Since the first cell has not been completely
 evaluated, PC would want to evaluate it, but of course it can not, since the
 first cell still refers to the second, which requires the value of the first.
 In situations like this, PC will simply use the current value of the second
 cell, as it can not resolve the circular reference.  Generally, circular
 references represent errors in worksheet construction, but you may find
 legitimate uses for them.

 When a circular reference exists in your worksheet, PC will display the "Circ"
 indicator in the status bar, and the address of a cell involved in the
 circular reference may be looked up in the Options Statistics dialog box.  You
 will never see the Circ indicator when Natural Order is disabled and row by
 row calculation is in effect.  Since calculation in this case does not try to
 evaluate precedent cells before dependents, circularity is a non-issue.

 DISK FILES THIS PROGRAM USES:
^FPC.EXE
^FPC.CFG
^FPC.HLP
^FDESKJET.INF
^FEPSON.INF
^FPRINTER.INF