Chart Type

The type of control chart you are adding or modifying. All control chart types are for variable data.

Individual: Displays each value of the material characteristic being measured

Median: Calculates and displays subgroup medians. They are used when it is desirable to give little weight to occasional wild shot values. The median chart should be used only when subgroup sizes are small since the efficiency of the median in estimating the true universe mean decreases with increasing subgroup size.

Moving Average: Calculates and displays the moving averages of subgroups

Moving Range: Calculates and displays the moving range of subgroups

Process Capability: Displays a normal curve superimposed over a histogram of data and several statistics

X-Bar and R: Displays the means and ranges of the subgroups. The X-Bar chart calculates and displays the mean of each subgroup. The R chart calculates and displays the range of each subgroup.

X-Bar and S: Calculates and displays the means and standard deviations of the subgroups. X-Bar chart calculates and displays subgroup averages. S chart calculates and displays subgroup standard deviations.

Note that if you select X-Bar and R and X-Bar and S charts, the system enables all the fields on the Secondary Chart tab page.

Subgroup Size

The number of data points to be collected per plot point for this control chart. For Median charts, the entered number must be between 2 and 25. For all other charts, the entered number must be between 2 and 30.

Max Plot Points

The maximum number of plot points displayed on this control chart. A number between 2 and 100 is recommended.

Max Data Age (days)

The maximum age (in days) of the data points to be used in the analysis and the chart display

Note that this field and the Max Plot Points field are interrelated.

Propagate Alarms

If selected, allows the system to generate alarm messages if some point on the chart is outside of the limits defined in SPC Chart Maintenance.

X Tick Label

Defines the type of labeling for each subgroup along the X Axis.

Sequential (1 to N): Displays a number starting at 1, and incremented by 1 for each subgroup

Time: Displays the time the data was entered

Date: Displays the date the data was entered

Date/Time: Displays the date and time the data was entered

SFC: Displays the SFC number for which the data was collected

X Axis Label

The label displayed along the X-axis of the control chart

Scale

Determines whether the chart's Y-axis scale is linear or logarithmic (based on powers of 10)

Control Limit Options

None: Control limits are not used.

Fixed: Control limits are fixed as specified by the user.

Calculated: Control limits are calculated from the process data and the sigma coefficient.

Note that the upper and lower control limits specify the threshold values at which the process output is considered to be statistically “out of control”.

Upper Control Limit

The maximum value above which the process is considered to be statistically “out of control”. It is typically set at three standard deviations above the center line.

Center Line

The mean of the values plotted on the chart.

Lower Control Limit

The minimum value below which the process is considered to be statistically “out of control”. It is typically set at three standard deviations below the center line.

Sigma Coefficient

The number of sigma, or standard deviations, used to calculate the upper and lower control limits

Upper Spec Limit

The maximum value above which the plotted value is considered to be “out of specification”.

Target

The specified (nominal) value for the characteristic being plotted.

Lower Spec Limit

The minimum value below which the plotted value is considered to be “out of specification”.

Trend Rules

The identifier of the group of rules used to determine if a manufacturing process is in a state of statistical control. These rules are used during the SPC analysis.