I'm trying to calculate the "average" no. of units sold per month per item. The divisor is not 12 but it depends on which months have at least 1 unit sold. So if we only sold at least 1 unit for 5 months in the past 12 months, then the formula would be total no. Of units sold/5. Is this possible? So far, I've got no luck with Average function or AVG in the formula.