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A
Assignable Cause	A cause that can be detected and identified as contributing to process variation.
Attribute Data	Data from counting process results such as number of units non-conforming per inspected sample, or number of defects per inspected sample containing n units. As opposed to measured data, attribute data has a discrete number of possible values. p, np, u and c control charts are used to track attribute data.
Attributes Chart	A control chart that tracks whether a process is in control by tracking attribute data, or data counted from the process. p, np, u, c charts are attributes charts.
C
c Chart	Control chart that uses number of defects per sample to monitor the stability of the process. Each sample contains n units, and contains c defects per sample (zero or more defects per unit). The value of n must be constant from sample to sample.
center line	A line on a control chart representing average long-term value of the statistic plotted on the control chart.
control	Front panel object for entering data to a VI interactively or to a subVI programmatically.
control chart	A charting method for determining the stability of a process; that is, whether or not a process is in a state of statistical control. Shewart control charts monitor process stability by plotting sample statistics against a center line and control limits.
control limits	Upper and lower limits on a control chart represent the amount of variation about a center line that can be attributed to chance causes for a given process characteristic. Control chart points that fall outside the control limits signal that the process is not in control and that some action should be taken. Control limits may be calculated from process data or from standard values.
Cp process capability index	A measure in sigma units of the process capability that is a ratio of the spread between the specification limits over the m sigma spread of the process variation, where m normally is 6.
Cpk centered capability ratio	A measure in sigma units of the process capability with respect to how well the process is centered relative to the specification limits, also known as distance to nearest specification.
current VI	VI whose front panel window, block diagram window, or icon editor window is the active window.
D
defect	A measured characteristic of a specific unit of product or service that prevents the unit from meeting a specification requirement or is otherwise undesirable. In a unit, one or more defects are possible, and many different types of defects are possible. A defect is also known as a non-conformity if the characteristic prevents the unit from meeting a specification requirement.
F
fraction non-conforming	The number of units in a sample not conforming to specification divided by the total number of units in the sample.
H
Help window	Special window that displays the names and locations of the terminals for a function or subVI, the description of controls and indicators, the values of universal constants, and descriptions and data types of control attributes.
Histogram	A graphical summary of data in which the individual values are sorted by the range of values into which they fall (also known as bins), and in which the number of individuals falling within a each bin is counted. The data is plotted by showing the number of values (frequency) in each bin.
I
in-control process	A stable process whose variation is due only to chance causes; that is, no assignable causes of variation are present.
individual observation	A single measurement of a process characteristic.
M
matrix	Two-dimensional array.
measurement data	Data that is a result of observations or measurements of a characteristic that has a continuous range. As opposed to attribute data, measurement data is not discrete. Any discreteness in measurement data is due to the resolution of the measuring device, not the characteristic.
moving Average chart	Control chart that uses the average of n successive individual observations from a process to track the stability of the process mean. This type of control chart is typically used when the sample size is 1.
moving Range Chart	Control chart that uses the range between n successive individual observations from a process to track the stability of the process variation. This type of control chart is typically used when sample size is 1.
N
natural process limits	The limits which contain a stated fraction of the individual observations in a population. For a normally distributed population, the stated fraction is typically the process mean ± 3.0 sigma.
non-conforming unit	A unit of product or service that does not meet a specification requirement.
normally distributed	If a process is normally distributed, expected values for individuals within the process population fall on a normal or bell-shaped curve.
np Chart	Control chart that uses the number of non-conforming units in a sample to monitor the stability of the process. The sample contains n units, and zero or more units may be non-conforming. The value n can be constant from sample to sample.
O
observation	A measurement of a process characteristic.
P
p chart	Control chart that uses the fraction of non-conforming units in a sample to monitor the stability of the process. The sample contains n units, and zero or more units may be non-conforming. The value n can vary from sample to sample.
Pareto chart	A chart of a set of counted or totalized characteristics in which the characteristics are ranked in order of their frequency of occurrence. In SPC, Pareto charts are normally used to evaluate relative contribution of assignable causes and prioritize corrective action.
plot	A graphical representation of an array of data shown either on a graph or a chart.
pop up	To call up a special menu by clicking, usually on an object, with the right mouse button.
pop-up menu	A menu accessed by right-clicking, usually on an object. Menu options pertain to that object specifically.
process capability	A measure of the ability of a process to produce product within specification, assuming the process is stable. Specifically the variability that can be expected for a given process characteristic with respect to the specification limits for the characteristic.
R
R (Range) chart	Control chart that uses the sample range R to track the stability of the variation in the process. Sample range is max sample value minus min sample value. Sample size must be 2 or more.
representation	Subtype of the numeric data type, of which there are signed and unsigned byte, word, and long integers, as well as single-, double-, and extended-precision floating-point numbers, both real and complex.
run chart	A chart of the individual observations in a set of samples plotted in time order of occurrence.
run rules	Rules applied to a consecutive set of points on a control chart, that are used to detect changes in the process such as out-of-control conditions, or process shift.
S
s (std dev) chart	Control chart that uses the sample standard deviation s to determine the stability of variation in the process. Sample size must be two or more.
sample	A set of measurements (observations) or units (from which counted data is taken) used as a basis for evaluating the process.
sample (or subgroup) size	For measurement data, this is the number of observations (or individual measurements) making up the sample. For attribute data, this is the number of units n inspected for the counted characteristic.
specification limits	Limits that define the range within which a product or characteristic conforms to specification or user requirements (also known as tolerance limits).
standard values	The known standard values for process range, sample standard deviation, mean, or sigma from which control limits can be calculated.
subgroup	A set of measurements (observations) taken from a larger set.
T
tier chart	A chart in which the individual observations in each sample are plotted vertically. It is a useful means of visualizing the variation or spread in each sample.
top-level VI	VI at the top of the VI hierarchy. This term distinguishes the VI from its subVIs.
U
u chart	Control chart that uses the average number of defects per sample to monitor the stability of the process. The sample contains n units, and contains c defects per sample (zero or more defects per unit). The value n may vary from sample to sample.
V
variables chart	A pair of control charts that track whether a process is in control by tracking mean and variability of samples of measured data. Variables charts include X-bar & s, X-bar & R, x & mR charts, and mX-bar & mR charts.
VI library	Special file that contains a collection of related VIs for a specific use.
W
waveform chart	A numeric plotting indicator modeled after a paper strip chart recorder, which scrolls as it plots data.
X
x (individual) chart	Control chart that uses the individual observations from a process to track the stability of the process mean. This type of control chart is typically used when sample size is 1.
X-bar chart	Control chart that uses the sample mean, X-bar, to track the stability of the process mean. Sample size must be 2 or more.