Cell references identify individual cells in a worksheet. They tell Excel where to look for values to use in a formula.
Excel uses a reference style called A1, which refers to columns with letters and to rows with numbers. The letters and numbers are called row and column headings.
In this lesson you'll see why Excel can automatically update the results of formulas that use cell references, and how cell references work when you copy formulas.
What happens if the value in a cell changes after a total is calculated?
Suppose it turned out that the 0.17 value in cell B4 under Total Acres was incorrect. It was actually 0.19 acres instead. You change that amont in one of the ways described previously and hit ENTER.
As the picture shows, when the value in cell B4 changes, Excel automatically updates the total in cell B6 from 0.65 to 0.67. Excel can do this because the original formula =SUM (B2:B4) in cell B6 contains cell references.
If you had entered specific values into a formula in cell B6, Excel would not be able to update the total. You'd have to change not only the figures in cell B4, but in the formula in cell B6 as well.
Note You can revise a formula in a selected cell by typing either in the cell or in the formula bar 
.