Jump Ball

Question
When does the umpire chop the clock on a jump ball.  The rules say when the ball is "legally touched."  When is it legally touched?  Is it on the centers tip, or is it when a player outside of the circle touches the ball?

Answer
According to the instructions to and for timers in th national federation of high school basketball rules:
START THE OFFICIAL TIMEPIECE WHEN:
1. A tossed ball is legally tapped when play is started by a jump.  
So the tip itself starts the clock.  Note that if using a shot clock it does not start until one team possesses the ball.  I recall a before teams alternated possession on jump bals where this was more important on jump balls 1-2 seconds left at their free throw line players would try to tip it in the basket off the jump ball.