• The frequency histogram is a very effective graphical and easily interpreted method for summarising data
• The frequency histogram is a fundamental statistical tool of SPC
• It provides information about:
  • the average (mean) of the data
  • the variation present in the data
  • the pattern of variation
  • whether the process is within specifications

  Example frequency histogram

Drawing Frequency Histograms

In drawing frequency histograms, bear in mind the following rules:

• Intervals should be equally spaced
• Select intervals to have convenient values
• Number of intervals is usually between 6 to 20
  • Small amounts of data require fewer intervals
  • 10 intervals is sufficient for 50 to 200 readings