Now that you've learned more about using cell references, it's time to talk about different types of references:
Relative Every relative cell reference in a formula automatically changes when the formula is copied down a column or across a row. This is why in the first lesson you could copy the January formula to add up February expenses. As the example illustrated here shows, when the formula =C4*$D$9 is copied from row to row, the relative cell references change from C4 to C5 to C6.
Absolute An absolute cell reference is fixed. Absolute references don't change if you copy a formula from one cell to another. Absolute references have dollar signs ($) like this: $D$9. As the art shows, when the formula =C4*$D$9 is copied from row to row, the absolute cell reference remains as $D$9.
Mixed A mixed cell reference has either an absolute column and a relative row, or an absolute row and a relative column. For example, $A1 is an absolute reference to column A and a relative reference to row 1. As a mixed reference is copied from one cell to another, the absolute reference stays the same but the relative reference changes.
Next you'll see why you'd use an absolute reference.