"Lean Math." Now, there's a name that evokes passion in the heart of every lean practitioner!?
But, the truth is effective lean transformations require some level of math, whether it's the often deceptively simple calculation of takt time, sizing kanbans, calculating process capability, or anything in between. It's hard to get away from math-free lean and certainly math-free six sigma!
Lean Math is not intended to be some purely academic study and it does not pretend to be part of the heart and soul of lean principles. Rather, it's a tool and a construct for thinking. Here we want to integrate lean math theories and examples with experimentation and application.
In the end, we hope the blog, along with its fledgling community, lives up to the tag line, "Figuring to improve."
Here's some often overlooked and misunderstood value stream mapping math.
The lead time ladder has two levels or “rungs.” The bottom rung is the process or processing rung on which the relevant process time is dropped down. This is usually pretty straightforward...unless there is a split or branch in the material, service or knowledge flow within the value stream.
When discussing lean math with other folks, I often get some less than optimal responses. Of course, much of the time it's probably me!
In any case, this is how I would characterize the more non-value-adding responses to the subject.
Lean quotes, 'laws' and Rules of Thumb; let's get a list going! How many can you add to this list?
A contribution from one of our readers - Troy Bourgeois from Flow Consulting
The 10X ROI (Productivity Improvements in parallel with Sales growth)
One of the things that I have noticed as I look out at the world is – things change.
The weather changes, the tides change, and customer demand changes.
Of these three, variation in customer demand is perhaps of the most interest to lean practitioners, because, after all, if customer demand were constant, the challenge of designing and managing the value stream would be much simpler.
So accepting that in most cases customer demand does change, a sensible follow up questions are: By how much? And is the demand at least stable?
We've all encountered a "Duh" moment when we're working with time units.
Many time the problem is that we forget that there really aren't 100 seconds in a minute.
That would be the decimal trap.
For example, 4:17 as reflected on a time piece (a.k.a. stopwatch) does not equate to 4.17 minutes. If for some reason, decimals are preferred, like on the “bottom rung” of a value stream map’s lead time ladder, then 4:17 should be reflected as 4.3 minutes. Calculated as follows:
Cycle time often seems like a pretty simple concept.
Until one tries applying it in the real world.
Over the next few weeks and months, we'll explore, in detail, the math surrounding the various members of the cycle time family. Until then, the figure below may shed some light on the subject!
Got asked what would happen to inventory when the number of stocking locations change. I thought for a minute and remembered a quick estimate. The Square Root Law states that total safety stock can be approximated by multiplying the total inventory by the square root of the number of future warehouse locations divided by the current number.
X2 = (X1) * √ (n2/n1)
n1 = number of existing facilities
n2 = number of future facilities
X1 = existing inventory
X2 = future inventory
Here are two examples:
