How to reset millis( )? I am currently doing a school project.  There you have to program a stopwatch with the Arduino.  I wrote a program where millis starts.  But when I press my start button, millis don‘t start from 0. 
Has someone an idea? Please let me know.

Ps: I‘m German, so I‘m sorry for my bad English
You don't. Instead you just remember what millis() was when you pressed your start button, then subtract that from whatever millis() is showing at any other point in the future.