What??™s a moving range?
Variation between successive values. Table 18.2 shows the count and mR value for
each month of the year 2002. The mR values (moving range) shown are the absolute
value of the difference between the count value for one month and the month
immediately prior.
We can then average the moving range, as shown on Figure 18.7. Add up all of
the moving ranges and divide by the number of months differentiated (11), and we
n
UCL = 16.929
LCL = 0.0
CEN = 5.182
??“5
0
5
10
15
20
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 18.7 Mo ing range chart for 2002.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
10 Count values 15 20 14 12 25 12 12 18 22 25 25
mR values 5 5 6 2 13 13 0 6 4 3 0
table 18.2 Count and Mo ing range Values for 2002
Statistical Process Control n 249
come up with 5.18 for our average moving range. The center line shows the average
moving range for Table 18.2. The upper limit is 16.93. The lower limit is always 0.0
for the moving range chart, since mR is an absolute value and an absolute value is
always either positive or zero.
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