Cells in Excel are referred to using relative or absolute references. A formula with relative references changes when the cell's position does. If, for example, a cell has a formula "=A1" ...

Running totals show how figures build over an extended period, one entry at a time, allowing you to see trends and patterns ...

If you omit the dollar sign, Excel applies the highlight to the cell instead of the entire row. The reference to row 3 isn’t absolute, so the rule can evaluate all of the rows in the selected range.