A simple search would throw up several threads such as:
http://www.flyertalk.com/forum/briti...0561-fqtv.html
Originally Posted by
UKtravelbear
I thought one was where you were crediting miles and the other for status?
So for example you could credit the avios / tps for the flight to BA but use your AA status if that was higher than your BA one.
There are 4 fields in total.