I have been considering purchasing some body armor. However, I am completely uneducated on the subject. Can I have a soldier or LEO here give me some education? I know that there is a difference between pistol-caliber rated and rifle-caliber rated. There is soft armor for pistol caliber, and plates with carriers for rifle calibers. But, what is the difference between I, II, III, and III+? Any help would be greatly appreciated. Thanks.