Hi Richard,

I know. It took me some time to see it too.
I reckon the simplest way to put it would be that the formula looks at one specific date and then counts the amount of mills that falls within this criteria. That's where the mistake happens. If we take the date, say 1st of march 2013 - the current formula will include mills where the date for commissioning and commercial operation BOTH are lower than 1st of March 2013.. In that way, the formula counts mills that are "in commissioning OR commercial operation" but doesn't distinguish between the two