Most impactful tool for your industry?

MacBook Pro, iPad and iPhones! We love the note features, and reminders. 

So far my most useful tool has been my plumbing code book. It's honestly been what has guided me to start my own business 3 months ago. I'm hoping that as long as I follow my code book I'll eventually get to be more successful. Right now my biggest problem is I don't have enough customers because I'm kind of in an economically depressed area but I'm within an hour of all four directions of access to tons more customers.