In addition to the informal stabilization of the process
previously discussed, there is a tension between having
a stable process and continual process improvement.
Continual improvement means the process data for
the previous process may not be valid for the new
process, and new natural process limits may need
to be recalculated on an ongoing basis. Even when
most changes are incremental, compounded small
changes can lead to dramatic improvements. Wheeler
observes that continual improvement is a journey
consisting of frequent, intermittent improvements,
interspersed with alternating periods of predictable
and unpredictable performance (Wheeler and Poling
1998; Wheeler 2003).