Try to avoid using numbers (actual data) in formulas. Instead use cell
references that point to data cells. By keeping a data item in a unique
location in the worksheet you can much more easily change the item and
have the change affect the use of that item throughout the worksheet.
Example: Cell E5 holds the data item 6%, that represents tax rate.
In all formulas that need to reference tax rate, refer to cell E5 instead
of typing in 6%. If the tax rate later changes to 6.5% you can change
the rate value one place in your worksheet. The value changes
in every formula that refers to that cell and you need not locate and
change every formula that uses the value.
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You may often need to reproduce a formula in several places in a worksheet.
In many cases, you can type in the formula one time and then copy it
to the other locations, avoiding hardtodetect typing errors. When
copying formulas, be sure to understand how to use relative and absolute
addressing, described below.
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Relative
& Absolute Addressing
For copied formulas, Excel uses relative addressing as the default.
That is, Excel adjusts the cell references in your source formula when
the formula is copied to new locations.
The worksheet above shows three formulas in cells D4, D5, and D6. Because
of this model's layout, there's no need to type in three formulas. Type
in just the first formula in cell D4 and then copy it to cells D5 and
D6.
This view of the same worksheet shows the contents of the formula cells.
You can see that for each copied formula, Excel adjusted the cell references
to refer to the data in the correct row.
However, there may be occasions when you want to override Excel's relative
addressing default. In the example below, the formula in the Tax column
makes use of the values in column D and the 5% value in cell B1.
The illustration below shows how the formulas appear. In order to properly
copy the formula in E4 to cells E5 and E6, absolute addressing must
be specified in the master formula in cell E4 for the 5% tax figure.
An absolute cell reference is indicated by putting a dollar sign before
the row and column reference. In the example worksheet above, cell B1
holds the tax value. When the cell reference is entered as $B$1 in a
formula it indicates an absolute references to that cell. As an absolute
reference, the reference won't change when the formula containing the
reference is copied.
So when the master tax formula in cell E4 is copied down the column
to cells E5 and E6, the reference to the tax rate remains correct, pointing
to cell B1. Note, however, that the first cell references in the master
tax formula (D4) is left relative. When it's copied in a formula, it
becomes D5 and D6, which is also correct.
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Keep formulas simple and straightforward. This makes them easier to read
and to debug. If you need to exress complex relationships, create several
formulas and use them like building blocks instead of constructing an
overly long formula.
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Use range names instead of cell references to make formulas easy to understand.
(See the discussion above on naming and applying ranges.) If you assign
a name to a cell or a range after you've used that cell or range
in a formula, use the Insert, Name, Apply commands to have Excel
use the name in formulas place of a cell reference. If you want the name
to be used in place of any reference to that cell anywhere it might appear
in the worksheet, select a single cell before issuing the commands. If
you want the name applied to only a particular range, select that range
before issuing the commands.
Example:
Formula without range names applied: =C10*A3
Formula with range names applied: =Subtotal*Tax
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Arrange your model to show intermediate quantities
of interest, such as subtotals.
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Try to plan the arrangement of worksheet formulas and labels so the flow
of calculations is obvious.
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