I've noticed that some referees wear two watches on the field, especially at the highest levels. I've also seen that one watch counts down while the other counts up. What is the purpose of the second watch? Is it a backup to track time elapsed, and then used for added time? I'm curious because I've only used one watch before, and want to see your tips for using the second watch. P.S. At what levels, in your experience, have you used added time for games?