Hi David
$ sign refers to absolute cell referencing, meaning when you autofill the formula (drag the formula down or across to populate other cells) the cell reference remains the same.
In this case, F$4 means that row 4 is locked in and won't change when autofilled.
Another example, if it was $F$4, then it would lock in column F and row 4.
Hope that helps?
Cheers
Damien
