I almost never use excel except as a glorified running total calculator, so bear this in mind as I try to go beyond that for the first time.

Let's say I have a range of manually entered numbers in a column, such as b8:b20. Now lets say I want to subtract the same figure from each cell, a number located in B1, and only after that operation is completed then get a sum for the range of cells in b8:b20. I would only want this subtraction to occur if the number is greater than 0 (to avoid a negative number within the range where a blank cell was). I hope that wasn't too confusing.

So how to I proceed?