152 THETOYOTAWAYFIELDBOOK
Begin with a review of the actual production or sales for each specific product
over the previous 12-month period. This will provide a high, low, and average
volume demand. The actual numbers can be plotted on a graph to get a visual
representation, which is better than the plain numbers because it’s possible to
see the “weighted average.” Simple highs and lows represent peaks, and a few
peaks may skew the average. Plotting the actual numbers on the graph allows
you to use your eye to see the most appropriate leveling point.
The final decision of the level volume is somewhat subjective. In general,
Toyota selects a number that is approximately 80 percent of peak demand
(unless the peak was an isolated event) because the gap between 80 and 100 per-
cent could be filled using overtime (eight hours per week). The determination
of leveled demand will be used to calculate takt time. In the previous chapter,
we discussed the use of takt time as a design parameter. When determining the
leveled demand quantity it is better to err on the side of a slightly higher
demand if you are uncertain or uncomfortable with the 80 percent level. In real-
ity, when you determine a quantity to serve as your assumed daily level
demand it will either be too high, too low, or just right (not as likely). The prob-
lem is, it’s difficult to determine initially because of the variation that has been
occurring in the production (a cloud). Once the process is stabilized, the clouds
clear a bit and the correct level will become more evident and adjustments eas-
ily made.
TIP
Identify the Most Important Items for the
Greatest Benefit
It may not be practical to level all products, due to extremely low
or sporadic demand of some items. Before beginning the analysis
to identify specific products to level, it may be necessary to isolate
variation (see Chapter 3) or to utilize an isolation technique we call
“slice and dice,” which is discussed later in this chapter. Identify
key products in key areas and begin with those that will provide
the greatest benefit.facility. After all, it has taken Toyota 50 years to achieve their current success,
and in many cases they’re still striving to reach the epitome. The key is to stretch
enough to make a great improvement, and to challenge your capabilities, but
not so much that total failure results.