His motives for volunteering lie somewhere on the 'continuum' between charitable and self-serving.
a 'continuum' of temperatures ranging from very cold to very hot
(..) You're alive. Bulletproof vest? How did you know? What about all that talk about screwing up future events? The space-time continuum? Well, I figured, what the hell. MARTY: So how far ahead are you going? About years. It's a nice round number. Look me up when you get there, all right? (..)1985 Back to the Future