“When you are recalculating the average because you see a shift, does the average from your previous calculation only take into account those values up to the new average? (not sure if this makes sense so I will ramble on a little bit more) Usually my average is calculated with 30 values…but if I see a shift before those 30 values appear, and I recalculate the average, should I only average the, lets say, 10 values I have collected? Or should I still have 30?”
Yes, I would go back and calculate the average and limits to include just those 17 data points in that timeframe. That clearly seems like a “different system” than the timeframes before and after that shift.
I wouldn’t include a data point in more than one calculation over time. You don’t need 30 data points if the timeframe for that system was only 17. You’re on the right track in how you’re thinking through this. “Only take into account those values up to the new average” seems correct.