Toyota Way Fieldbook : A Practical Guide for Implementing Toyota's 4Ps

Figure 14-7 shows the detail necessary to understand the daily characteris-
tics of the problem. The performance of this fabrication process varies from day
to day within a range. This process has not reached a level of stability, and the
variation indicates the possibility of multiple issues contributing to the instabil-
ity, thus representing a more challenging problem to solve.

336 THETOYOTAWAYFIELDBOOK

Fabrication Daily Units per Hour

0

1 2 3 4 5 8 9 10 11 12 15 16

5

10

15

20

25

30

35

40

Date

Units per Hour

Goal = 36

Fabrication Daily Units per Hour

20

1 2 3 4 5 8 9 1011121516

22

24

26

28

30

32

34

36

38

40

Date

Units per Hour

Goal = 36

Figure 14-7. Chart with sufficient date points to see trend

Figure 14-8. Chart with inflated appearance of variation due to scale

Figure 14-8 shows the same data as Figure 14-7 but the variability of perform-
ance is artificially inflated due to a compressed scale on the chart. Visually, the
problem appears larger than it truly is. It’s important for a chart to have the correct
visual impact so everyone has a clear understanding of the challenge ahead.

Figure 14-9 shows the same data as Figures 14-7 and 14-8. Notice how the
variation is visually smoothed. This process appears more stable, and thus is
misleading. An excessively large scale causes the artificial smoothing effect.