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David,
Even though lead time is now often used for what used to be called
cycle time, the old use of lead time is still common, so this means
that lead time now has two meanings, just like cycle time. Which
makes *lead time* as useless as *cycle time* in common discussion.
Defining the terms at the beginning of a discussion would not clear
up the confusion for someone who uses lead time to mean how long it
going to take to get the roofing trusses on site.
If you think hard about it, lead time for trusses to arrive is the
same as lead time for something being in a queue, but personally I
can't make the translation in my mind fast enough, having spent too
long in production and inventory control. I do not equate the lead
time of something coming into my line to the service time (formerly
known as cycle time) of something going through my line.
Anyway, time-in-queue, which I (now) choose to call *service time*
is the time we find in Little's Law. It is this time that is
directly proportional to inventory.
Mary Poppendieck
--- In [email protected], "David J. Anderson"
<netherby_uk@y...> wrote:
> Mary,
>
> Thankyou for this - very enlightening.
>
> Throughout my own manuscript I have used "lead time"
> for your "cycle time". I may have to consider changing
> this - or perhaps just define the usage at the
> beginning.
>
> There is no doubt that in common usage there is some
> ambiguity in the use of these terms.
>
> Cheers,
>
> David
>
>
> >The mystery was cleared up when I pulled out the
> >operations
> >management text book I taught from a couple of years
> >ago (Krajewski
> >& Ritzman, 5th edition). Here they had a long
> >discussion of cycle
> >time which was clearly the same as takt time, and
> >then in a footnote
> >they said:
>
> >"Except in the context of line balancing, *cycle
> >time* has a
> >different meaning. It is the elapsed time between
> >starting and
> >completing a job. Some researchers and
> >practitioners prefer to use
> >the term *lead time*."
>
> >SO! Cycle time has TWO commonly used meanings Eone
> >takt time and
> >one equivalent to time-in-queue.
>
>
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