I am working on a spreadsheet to enter purchases. I will have probably have 25-30 cells with a case quanity and a total dollar amount for the purchase. To prevent errors in entering I want to either have a message box notify the user of the incorrect entry and change the cell color or display the message box of the error and then clear the cells contents. To do the above I will need for each cell(say column b, rows 10 to 40) to divide its entry($100.00) by column c, rows 10 to 40) their entry(4). So I will need for b10/c10,b11/c11 and so on. The error I am looking for will be a difference of 10% in the case cost. I will probably have to have a column for the start up case cost so that each time the user makes an entry it will check his/her entry against the case price. So i will have row b as the qty., c as the dollar amount, and say e as the initial cost/case. Will I need to write a conditional format code for each cell or use the worksheet calculate event?