Many people have been having trouble with a small aspect of HW#3, so I thought I would write this up. In the homework, you are assigned to create a formula computing monthly totals and are then supposed to copy that formula down the column. However many of you have realized that when doing so, things go awry. This is why:

A cell reference like C3 or D9 is what is called a "relative cell reference" meaning that when you copy a formula from one location to another, the cell references in it will be shifted relative to the difference in locations. You copy a formula down one row, the references in it get bumped down row, etc. This is correct behaviour (in that it follows the manual). The thing to note is that there's another kind of cell reference -- "absolute cell reference" -- something like $C$9. Basically, if you put a dollar sign in front of the column specifier, the column won't change when you copy the formula. Same for row. And you can put dollar signs in front of both column *and* row, to make sure the reference stays constant whenever you copy the formula anywhere.

If you still have questions about this, feel free to email me