For ammo, that's the answer. Thanks. But for trucks, gasoline, military services, military supplies, and I don't know whate else, it's not so easy.
If I buy only one kind of weapon, I can see how much usage goes up by and know the effect of that weapon. I suppose if I buy the exact same two kinds of weapons for two months, I could do some algebra and get the net for those two weapons, etc.
But is there any way to know the increase per weapon without spending several game years testing?
And even for ammo, there's something weird going on. I have all my offensive weapons deactivat4ed. But I'm still showing non-zero (albeit low) monthly usage of their ammunition.