Conditional Formatting - comparing worksheets

Hi,
I have 2 worksheets - one is a monthly update, the other is last month's data.

I want to highlight the changes on the monthly update sheet using conditional formatting.

I named the columns as ranges on the "last month" worksheet, and then used =Match(A1,Jan,0) (wheras Jan is the range on the "last month" worksheet where A1 resides)

What formula do you use to say "if A1 does NOT match a value in range "jan", then format it"?