Talk:Affinity/@comment-178.203.233.84-20161004094552/@comment-8256051-20161004101133

^ Wammut is correct.

For the precision, when an ally kills an enemy within affinity range, you get 25% affinity on your warframe and 75% affinity spread equally between all your other weapons (thus 25% each if you have primary+secondary+melee). Which explains why people often only take one weapon to lvlup faster (but it only works with weapons).

Also note that mission objectives and challenges reward affinity the same way ally affinity does.