What it shows
Monthly failure cost (internal plus external) with its mean and control limits: mean plus or minus 2.66 times the average month-to-month change, from the baseline months (shaded).
Why it matters in manufacturing
Failure cost always moves a little. A control chart shows which months moved more than normal variation explains, so you investigate real signals and leave noise alone.
How to read it
Points in the danger colour lie outside the limits: something specific happened that month. Points inside, however high, are normal variation of the process as it is; lowering them needs a change to the process itself.
What good looks like
All recent points sit within the limits around a mean that has come down after an improvement: the process is stable and predictable at a lower cost.