The
Shepherd: Early Warning Indicators
The primary indicator monitored by the Shepherd is the
number of inactive lots. The chart below shows the total
WIP and inventory age at the start of each 12 hour shift
(over a one-week period), filtered to only include lots
that have been in queue at their current operation for at
least 12 hours (defined as inactives). This chart clearly
shows a rise in the number of inactives beginning during
the night shift on May 23rd, and continuing for several
days.
In practice, the Shepherd would be monitoring the
number of inactives on an ongoing basis, in addition to
looking retrospectively across the current week. For
example, the chart below shows the number of
inactives and the total inventory age for each area
during the peak of the WIP bubble shown above. The high
WIP in the Photo area is not unexpected, given known
problems at the 5xStep tool group shortly prior to this
time (as described in the
Traffic Cop example). However, the high number of
inactives in the Strip area bears further investigation.
The next chart shows the inactive lots in queue in the
Strip area at the peak of the WIP bubble. At 6:00 am on
May 25th, there are four lots that have been waiting in
queue at their current operation for 39 hours.
The Shepherd continues by investigating one of these
lots in more detail. (Go to the
next page.)
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