Conditional Formatting Issue with several rules for one cell

OK, maybe I'm just not getting it. Work just switched to Windows 7 and Excel 2010 from XP & 2003. I usually can figure things out but I just can't see the logic and an hour on the net forums has been fruitless.

I need a simple indicator in a financial spreadsheet. In prior Excel, I could write 3 conditional format formulas for one cell, i.e. > 0, = 0 and < 0 would be green up arrow, side yellow arrow and down red arrow, and I could determine the condition formula, i.e. Last_Sales -This_Sales as the criterion.

I now have a simple columnar sheet, say Last_Sales in Col A, This_Sales in Col B, and a narrow Col C where I want the arrows to go. Col C will have no values or formulas - I just want the arrows visible there. The criterion above should be used.

What are the steps to get this done in the Excel 2010 Ribbon / Conditional Formatting tab?

Many thanks in advance.