What is Control Chart?
Control Chart
A picture where the values are drawn every day and the usual width is drawn with a line to see if it has changed from usual.
What it means
A control chart is a drawing in which measured values are plotted in chronological order, and the range where the values usually stay is drawn with up and down lines. If the dot goes beyond that line, something has changed.
If you only look at pass and fail, you only know after the defects come out. A control chart tells you that something is “changing” while it is passing.
At the pen factory
The thickness of the line drawn with refill was usually 0.48 to 0.52 mm. On the 23rd day, 0.54mm came out. It passed (0.45~0.55), but it was outside the usual range, and that day was the day I changed the ink tank.
Why it matters
You can take action before defects appear.