ITEE ITEE-1 | Page 35

Reference Control chart scheme Plotting the measured data will reveal process irregularities when points fall outside the bounds or are clustered on one side of the centerline. ●Control chart A “control chart” expresses the status of work processes using a line chart. For example, the chart here shows irregular points based on the following criteria: • Any points outside the control bounds, either high or low • If there are six or more points in a row above or below the centerline, the sixth point and beyond. Based on these criteria, there are three points judged to be irregular in the example chart. Irregularity out of bound Upper control bound Upper limit Centerline Median data value Lower control bound Lower limit Irregularity biased to one side of median ●Histogram A “histogram” is a method for representing the number of elements in each group as a bar graph, dividing totaled data into some number of groups. A histogram can reveal an overall picture of the data, the central position, range of variation, etc. For example, this chart shows the results of a survey of cellular phone owners in a certain city broken down by age group, revealing that cellular phones are most common among people aged 21-30, followed by people aged 10-20, then 31-40, and that they were least common among people aged 51 and over. Number of people Number of cellular phone owners (City X) 50 40 30 20 10 ∼ ∼ ∼ 29 ∼ 10 or less 10 21 31 41 20 30 40 50 51 Age bracket or more