7. SPC Control: Bar Chart

Display options are available for Histograms and Pareto charts on the Bar Chart tab in the SPC Control Properties dialog box.

The chart that is selected on the Chart tab will be enabled.

  • Histograms
  • Pareto Charts

Histogram Charts

The Histogram chart is available for Variable properties. It is particularly valuable when setting up/adjusting your system and determining appropriate specification limits for the process.

1 Show spec limits.
2 Show normal curve
3 Max samples
4 Show info box
1 Show spec limits

Displays/hides the specification limits (USL/LSL).

Check Displays the specification limits.
Clear Hides the specification limits.
2 Show normal curve

Displays/hides a normal distribution curve.

Check Displays a normal distribution curve
Clear Hides the normal distribution curve.
3 Max samples

Maximum number of samples that will be used to create the curve.

Note:
  • The samples that are selected are based on the:
o Duration selection on the General tab in the SPC Control Properties
o Sampling parameters selected in the General tab in the Variable Quality Characteristics Properties dialog box.
  • The actual number of samples may be slightly larger than the entered number. For example, if 40 is entered, the actual number of samples may be 40.2.
4 Show info box

Displays/hides a list of values calculated for the Histogram.

Check Displays the info list.
Clear Hides the info list.
Note:
The information/values that display are:
  • Cp metrics
  • Cpk metrics
  • USL (Upper Specification Limit)
  • LSL (Lower Specification Limit)
  • Mean
  • Range
  • Sigma
  • Samples (Number included in calculations)
  • Zusl score
  • Zlsl score
  • ZBench score
  • Median

Pareto Charts

The Pareto chart provides a visual gage of the number of selected Defects that occur in the process. Visual aids can be selected, as follows.

1 Show fixed number of bars Check or clear to do the following.
Check Displays the number of bars entered in the field.
Clear Displays the number of bars for all defects that have values greater than 0.
2 Show bar of remaining defects Displays a bar that:
  • Reports the total of all defects that are not included in the defect categories for the  bars that display in the chart.
  • Is labelled O (for English systems).
3 Show info box Displays/hides a list of defect names/descriptions that are included in the Pareto chart.
Check Displays the info list.
Clear Hides the info list.