Thanks I have managed to add some formulas, after reading your articles, to some of my columns.

I have run into another problem. I want to add a formula to a row. I have an invoice with 6 columns, the first is Qty, the fourth is Unit Price, the Fifth is Discount and the sixth is Line Total. My first row has headings and the second has amounts. I want to multiply Qty by Unit Price and Subtract the Discount column. I have tried putting in some formulas but they don't work?