Someone help me using Excel VBAProject to write a formula: Function mySum(firstCell As Range, interval As Integer, lastCell As Range) temp = 0 For i = firstCell.Row To lastCell.Row Step interval temp = temp + Cells(i, firstCell.Column) Next i mySum = temp End Function This is formula under Module1. End line of Excel sheet, I enter :" mySum(c5,9,c275)". Because I want adding every nine line number togather ( example = c5+c14+c23+c32 ... until to +c275 ). Now this formaula is working. but problem is -- this formula can not auto update, this mean that every time I change or add new number, it can not sum and make new sum ( still keep old sum number ). I have to re-enter " mySum(c5,9,c275)" and enter, then new sum came out. I don't know what is wrong? I don't know how to fix this problem ? It shall auto update by that formula. Someone told me I need setup run macro into module1. I don't know how to do this let run macro into module1 ?

What is the "9" in there for? Larry Today seems like a good day to chew through the restraints.