An old timer in Bakersfield showed me how he checks for crown on a board by eye

Stopped by a jobsite in Bakersfield about 3 weeks ago to pick up some trim I'd ordered and got talking with this older guy named Walt who's been running trim crews for 40 years. I was about to run a 12 foot piece through the miter saw when he put his hand on my arm and said "hold on, look down the edge first." He had me sight down the length of the board against the light and showed me how you can spot a bowed or crowned board before you ever make a cut, just by getting your eye level with the edge. I'd been trusting the factory edge and fighting gaps for weeks on that job. Now I check every stick before it goes on the saw. Anyone else got a quick check they do before cutting that saves them a callback?