When a formula is copied, Excel increments all the cell references relative
to where the formula is copied to. Hence, A1 would be a "relative
reference". Sometimes, we don't want this to happen, so we create an
"absolute reference" by adding the $ symbol. $A$1 will not change when it is
copied. By placing just one $ symbol, you can lock just the row or column
portion of a reference. Thus, $A1 would keep column A, but increment the row
number when copied. A$1 would keep the row number, but increment the column
when copoied.
HTH,
Elkar
