Tight describes low variation: a tight process clusters close around its mean, a tight distribution shows a narrow histogram, and a tight spec leaves little room. Engineers say a process is tight but off target when the spread is fine and only the centering is wrong, which is the easy case to fix. A distribution called wide, fat or sloppy has too much spread, and that usually takes a real process change.
New pad is tight, sigma halved, but it's sitting 30 angstroms high. That's just a retarget.
Also heard as
- tight distribution
- tight process
Related terms
Standard deviation
Typical distance of individual values from their mean, the basic measure of spread, written as sigma or s.
Cp
Process capability ratio: the specification width divided by six process standard deviations, ignoring centering.
Cpk
Process capability index that accounts for centering: distance from the mean to the nearest spec limit in units of 3 sigma.
Process capability
How well a stable process's natural spread fits inside the specification limits, usually expressed as an index.