create a Counter which adds +1

I'm guessing this is related to the MonthIndex you were asking about in that other thread. Even if it is not you should still be able to use the same pattern. That's the only way I could come up with of sequentially incrementing a previous number that only changes on arbitrary rows. ImkeF might have another method though. I'll have to try that one out.

Edit: now that I've said that, I just came up with a way to do it in DAX. See the link for the solution. I don't want to clutter up this thread with extra code if that solution doesn't quite apply to this question.