Individuals chart with limits and signals.
Use it to tell real process changes from normal noise. Paste measurements in time order, and it calculates the limits and flags points outside them, runs of eight and trends of six.
Paste a single column from Excel. Use at least 20 points for stable limits.
Limits = mean ± 2.66 × average moving range (individuals chart). Signals checked: a point outside the limits, eight points in a row on one side of the mean, and six points in a row rising or falling. Recalculate limits only after a real, confirmed change to the process.
A control chart plots a measurement over time with a centre line and upper and lower control limits calculated from the process's own variation.
Daily fill weights average 500.2 g with an average moving range of 1.5 g, so the limits are 496.2 g and 504.2 g. A reading of 505.1 g after a nozzle change is outside the limits and points to a special cause to investigate.
An individuals and moving range chart, used when you collect one measurement at a time rather than in subgroups.
For an I-chart, upper and lower limits are the mean plus or minus 2.66 times the average moving range between consecutive points.
A point outside the limits, or patterns such as eight or more points in a row on one side of the centre line.