We were told two different things in our Primary check in brief.
1. API accounts for .5% (one half of one percent of your primary grade). This and your PRT score should make up 1% of your NSS.
2. API accounts for none of your NSS and is only used as a factor if you and another person are up for the last slot in a platform with the same NSS.
Basically, just get through it, its not that hard, aside from NAV. That test is just to easy to screw up. I acctually did very well but I walked out of the exam terrified that I failed.