It shouldn't be too challenging to apply Nelson rules to 100k lines, but the point of statistical process control is continuous monitoring--if you weigh yourself every day, you would look at the two-week trend every day, for example. Writing a script that checks if any of these rules are violated and emails you the graph if that's true seems simple and potentially useful.
I think what Elo's friends mean is that the constants hard-coded into Nelson's rules reflect some assumption on sample size. With a big sample, you'll violate them all the time and it won't mean anything. But they are a good starting point for tuning the thresholds.
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