I always shifted with a tach. Going to a shift light took a little getting used to. Still use the tach in the water. Defiantly use it to stage on the foot brake. Also nice to catch if the light malfunctions. I'd say every shift and starting line is usually within 50 rpm. For those of you that go "by ear". Maybe you shift early and you run a high torque motor that doesn't care. Or you miss it late slowing it down. I doubt it its very consistent. How do you stage? Bet it doesn't run back to back .00X second
Doug