THanks I did already have a look at the Microsoft guide, but the bit I don't really get (and which isn't explained there) is your multiplication of functions applied to two arrays before sumproduct-ing them with the third array. What does the multiplication do in this instance?

i.e. sumproduct(fx(array1)*fx(array2),fx(array3))

And yes I do find it hard to believe that you only dabble in Excel. Can't imagine the sort of shenanigans you must achieve in Word ;-)