OpenOffice.org OpenOffice - 3.3 Základní průvodce stáhnout pdf (Strana 161)

Error-checking formulas

Adding up columns of data or selections of cells from a worksheet often results in

errors due to omitting cells, wrongly specifying a range, or double-counting cells. It is

useful to institute checks in your spreadsheets. For example, set up a spreadsheet to

calculate columns of figures, and use SUM to calculate the individual column totals.

You can check the result by including (in a non-printing column) a set of row totals

and adding these together. The two figures—row total and column total—must agree.

If they do not, you have an error somewhere.

Figure 140: Error checking of formulas

You can even set up a formula to calculate the difference between the two totals and

report an error in case a non-zero result is returned (see Figure 140).

Creating formulas

You can enter formulas in two ways, either directly into the cell itself, or at the input

line. Either way, you need to start a formula with one of the following symbols: =, +

or –. Starting with anything else causes the formula to be treated as if it were text.

Operators in formulas

Each cell on the worksheet can be used as a data holder or a place for data

calculations. Entering data is accomplished simply by typing in the cell and moving to

the next cell or pressing Enter. With formulas, the equals sign indicates that the cell

will be used for a calculation. A mathematical calculation like 15 + 46 can be

accomplished as shown in Figure 141.

While the calculation on the left was accomplished in only one cell, the real power is

shown on the right where the data is placed in cells and the calculation is performed

using references back to the cells. In this case, cells B3 and B4 were the data

holders, with B5 the cell where the calculation was performed. Notice that the

Chapter 7 Using Formulas and Functions 161

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OpenOffice.org OpenOffice - 3.3 Základní průvodce Strana 161