From the archive
Day 14
Monday, 17 August 2026
Catch a batch drifting out of tolerance
The average can sit dead on target while the batch itself is out of control. STDEV is what actually says so.
Task:
You do quality control on a machine shop floor. Six bolts were pulled from this morning's run and their diameters measured in mm — the target is 8.00mm, but the real question is how consistent the batch is, not whether the average happens to land near it. Work out the average diameter in B8, the standard deviation in B9, then in B11 report whether the process is "In control" or "Out of control" by comparing the standard deviation against the tolerance in B10.
The daily challenge is part of Pro
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Recent days
The last 14 days. Today's challenge is free while your streak is alive; Pro opens every past day too.
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