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Control limit. A line (or lines) on a control chart used as a basis for judging the significance of the variation from chart point to chart point. Variation beyond a control limit is evidence that assignable causes are affecting the process.
Control limits are calculated from process data and are not to be confused with engineering or administrative specifications.
A control chart usually displays a lower control limit (LCL) and an upper control limit (UCL).
管制界線。
用在管制圖中當作點到點之間變異的衡量基準。
超出管制界線的變異可以證明某些原因會影響製程。
管制界線是從製程的資料來計算，不要和規格界線混淆。
通常管制圖會顯示管制下限 (LCL) 及管制上限 (UCL) 。
註 : 一般而言，UCL 與 LCL 的位置為平均值的正負三個標準差。
 

製程準確度：Ca
The deviation of the process mean from the midpoint of the specification limits.
衡量製程之實際平均值與規格中心值之一致性自生產中所獲得產品資料的實際平均值與規格標準值間偏差的程度。
 

製程精密度： Cp / Capability of process.
The greater the number, the better the process is capable of meeting the specification limits.
A process is judged to be capable when CP is at least 1.0.
衡量製程之變異寬度與規格公差範圍相差之情形。
一般而言，CP 至少大於一才可以開始量產，否則因變異產生的成本會過高。
 

製程能力指數： Cpk
Process Capability index related to both dispersion and centeredness.
關於分散與集中的製程能力指標。
同時考慮變異寬度與製程標準值之綜合性製程能力指標。
綜合 Ca 與 Cp 兩值之指數。
 

CpL
Distance between the process mean and the lower specification limit scaled using the capability sigma.
製程標準值與規格下限之間的差距值。
 

CpM
Process capability index that is affected by the difference between the sample mean and the target value.
受樣本中心值與規格中心值之差所影響的製程能力指標 。
 

CpU
Distance between the process mean and the upper specification limit scaled using the capability sigma.
製程標準值與規格上限之間的差距，通常用在單邊規格。
 

CR
The reciprocal of CP. The smaller the number, the better the process is capable of meeting the specification limits.
CR*100% is the percentage of the specification band used up by the process.
CP 的倒數。這個數愈小，製程愈能和規格限制相交。 CR 百分比則代表製程中所耗損的規格寬度。
 

Pp
Most commonly used process performance index.
This is a more reliable measure of process performance for folded normal distribution since folded normal distribution is one-sided.
此為對於交叉常態分配更可信賴的製程能力量測指標，因為交叉常態分配呈現單邊分配。
 

PpK
Process performance index related to both dispersion and centeredness.
This index is not suitable for folded normal distribution, which is one-sided.
同時考慮變異寬度與製程標準值之綜合性製程能力指標。
但，這指標不適合交叉常態分配，因它是單邊分配。
 

PpL
Distance between the process mean and the lower specification limit scaled using the process standard deviation.
This index is not suitable for folded normal distribution, which is one-sided.
製程標準值與規格下限之間的差距值。
但，這指標不適合交叉常態分配，因它是單邊分配。
 

Ppm
Process performance index that is affected by the difference between the sample mean and the target value.
受樣本中心值與規格中心值之差所影響的製程能力指標
 

PpU
Distance between the process mean and the upper specification limit scaled using the process standard deviation.
This index is not suitable for folded normal distribution, which is one-sided.
製程標準值與規格上限之間的差距。但，這指標不適合交叉常態分配，因它是單邊分配。
 

PR
PR. Reciprocal of PP.
PP 的倒數
 

峰度 Kurtosis
A measure of peakedness.
The population kurtosis is given by the fourth moment over the square of the variance.
This ratio equals 0 for any normal distribution.
A positive ratio indicates an excess of values in the neighborhood of the mean
(with a depletion of the “flanks” of the curve representing the distribution).
and a negative ratio corresponds to a curve with a flatter top than the normal curve has.
尖峰的量測指標。
最常用的峰度是四倍的動差乘上變異數的平方。
對於任何常態分配而言，這比率為 0 。
正機率意指超出平均數的鄰近值，而負機率則指超出常態的曲線。
 

偏態 Skewness
A measure of departure from normality.
A distribution is skewed if it isn’t symmetric but has more cases (a “tail”) toward one end of the distribution than the other.
If the tail is toward larger values, the distribution is positively skewed, or skewed to the right.
If the tail is toward smaller values, the distribution is negatively skewed, or skewed to the left.
衡量從常態分配的偏移量。
若分配不勻稱則會偏斜，朝向某一邊，呈現單尾。
若偏向較大的值，則分配呈現正偏差，反之則呈現副偏差。
 

四分位距 interquartile range, IQR
四分位距指在第1四分位數Q1、第2四分位數Q2以及第3四分位數Q3中，將其中數值最大的Q3減去數值最小的Q1，即Q3 − Q1。