I was the timer and scoreboard operator at the local high school for ~4 years. This is what got me the itch to try refereeing. Looked like fun
at the time. Its all about attention to detail.
I am also still the clock guy at home football games. When the school first installed play clocks they hired a guy to just run them (at the same pay of course) That first year was the only year we had two of us. My elbow was raw from all the nudging to start the damn thing. Guy just couldn't pay attention
So I practiced doing all three (clock, play clock, down/distance/LOS) during lower level games. The next year and ever since I've been by myself. The PA guy does his job by himself sans spotters and does a mighty fine job as well.