Excel supports three types of cell referencing, which are as follows:

1. Relative Every relative cell reference in formula automatically changes when the formula is copied down a column or across a row. As the example illustrated here shows, when the formula is entered (= B4 — C4) in Cell D4 then this formula copied in D5 then it will change into (= B5 — C5) related to the cell. 

2. Absolute An absolute cell reference is fixed. Absolute references do not change if you copy a formula from one cell to another. Absolute references have the dollar sign ($) like $S$9. As the shows, when the formula =C4*$D$9 is copied from the row, the absolute cell reference remains as $D$9. ‘ 

3. Mixed A mixed cell reference has either an absolute column and a relative row, or an absolute row and a relative column, e.g. $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.