what is the difference between chronograph automatic watches?

Answer 1

This question is way too vague to answer.
In general there are two main technologies:
Battery+Crystal operated - cheaper but you change the battery every 3-4 years
mechanically (gravity) operated. More expensive but use hand motion to wind the watch
For specific feature differences you need to check their specs

Answer 2

Even the defense force would not define an attack rifle as a totally computerized weapon, and the BATF defines the totally computerized variations of the m-sixteen as device weapons. So get your head out of your buttocks.