This has caused some problems over the last 6 or so years as NCAA rules have enacted the 40 second play clock, replay, 10 second reduction and other rules that are not suitable for high school football quite yet either due to expense or practicality. What we use in Texas for timing is from the 2005 rule book, which is certainly confusing to the new members.
I think it is almost time for Texas to develop their own rule book or work with NFHS to make significant changes and adopt their rules. I can't believe I just said that.