Hi!
I am trying to sum monthly unit sales data into quarterly. I have used previous thread and advice in that thread which was SUM(OFFSET('Monthly Sales'!P$3,ROW()*3-9,0,3,1))
Somehow this formula is missing out some data and I dont know why. Because I dont understand the offset function I cannot figure out how to fix the problem. Your advice will be appreciated.

Cheers,
Elmira