Starting the Clock on Jump Ball

[WAZebra]

I have always started the clock when a non jumper touches it. Is it legally touched when a jumper taps it or when a non jumper touches it? The rule book states that the clock starts when the ball is legally touched. I consider this a rather embarassing question, but please tell me where I can find somewhere in my rule book, case book, simplified rules or officials manual a reference to when the clock should be started on a jump ball or when the official should chop the start the clock signal.