Note: This may be the most important technique in the entire book. I once had a manager who entered every formula in every data set by hand. I didn’t have the heart to tell him there was an easier way.
Strategy: You need to indicate to Excel that the reference to C1 in the formula is absolute. You do this by inserting a dollar sign before the C and before the 1 in the formula. For example, you would change the formula in F4 to =ROUND((D4*E4)*$C$1,2).
As you copy this formula down to other rows in your data set, the portion that refers to $C$1 will continue to point at $C$1, as shown below.
Figure 188 The dollar signs keep C1 pointing to C1.