Acha Bacha

Apples

Apples

I see a red ball up in the tree.

I feel the Apple smooth skin.

I taste a juicy Apples.

I heer the bees buzzing in the Apple tree.

I smell fresh Apples in the tree.

       

Kids Little poem

Red Roses

Roses are Red,

Violets are Blue,

Sugar is Sweet,

And so Are You.

       

Morning Poem

Why I don't use Cycle Time in Kanban

Why I don't use cycle time in Kanban from Andy Carmichael

These slides were produced in response to a request for a brief summary of the terms I use for describing flow systems, particularly in a Kanban context. Along the same theme also see The difference between Cycle Time and Lead Time, More Musings on Little's Law, Visual explanation of Kanban terms and In search of unambiguous terminology for Flow systems.

What is there to be afraid of?

What is worthy of our fear? Is Death? Surely not. He who lives will die, and such inevitability must be respected and known, yet not cause dread. No more fear taxes, since he who earns can scarce keep it all, can he, any more than he can take it with him? For what purpose would you keep it all? I grant you death and taxes should be avoided - where it's possible to do so with honesty and honour. But they are not worthy of our fear.

Maybe boredom is a more suitable object. To live an uninteresting life is both eminently possible and profoundly fearful. Don't you have a mind though, and doesn't it engender imagination? And is it beyond that imagination to find an action, project or enterprise that could engage you in some means of improving your own or your fellow's lot? Boredom is not worthy of fear, since it is easily remedied.

Yet I think there is an entity worthy of fear, fear true and cold. It is waste... the waste of human potential. Such waste inhabits every corner of life where ideas spring up and are swallowed, spontaneously springing to life and dying like fundamental particles separating and colliding undetectably in the depths of space. Waste of human potential is omnipresent. It occurs in places of learning, and places of work, in families and in churches, in friendships and in war. It steals not only from those whose potential is untapped but from their communities, their

 relationships and indeed all society.


Fear this waste. Yes. Fear it and fight it.

More Musings on Little's Law

My previous posting about why not  to use Cycle Time in Kanban resulted in some interesting discussions, and I'm grateful to +Steve Tendon for pointing me in the direction of this paper [1] by John D.C. Little and Stephen C. Graves which gives some very helpful historical background into the derivation of Little's Law, its applicability and some of the terminology used.

From Little and Graves (2008)

Little's own formulation of the "law" was as follows:

L=λW

where

L = average number of items in the queuing system,
(equivalent to WIP in Kanban terminology)

W = average waiting time in the system for an item,
(equivalent to System Lead Time)

λ = average number of items arriving per unit time
(equivalent to Delivery Rate, assuming "stationarity")

With Kanban preferred terms we can see this maps to:

WIP =  Delivery Rate * Lead Time
or
Delivery Rate = WIP / Lead Time

Little used "waiting time" for the time taken by one unit to traverse the system (W) because his original context was queuing systems. For other applications he suggested Flow Time, which I think is a very useful alternative.

He also notes though that other authors use other terms for W, including cycle time, throughput time, and sojourn time, depending on the context. Yes - cycle time I'm afraid is in that list which is why confusion still abounds. This conflicts with the more generally accepted definition of cycle time in manufacturing, which corresponds to the target rate of working expressed as Takt Time, and is the reciprocal of Delivery Rate. In other words this confusion of terminology is at least as old as the reference Little and Graves cite: Factory Physics by Hopp and Spearman (1st edition:1996).

Useful background, but the message to me is still: "Don't use Cycle Time in Kanban!".


References:

[1] Little, J. D. C and S. C. Graves (2008). Little's Law, pp 81-100, in D. Chhajed and TJ. Lowe (eds.) Building Intuition: Insights From Basic Operations Management Models and Principles. doi: 10.1007/978-0-387 -73699-0, (c) Springer Science + Business Media, LLC http://web.mit.edu/sgraves/www/papers/Little%27s%20Law-Published.pdf

[2] Hopp, W. J. and M. L. Spearman (2000). Factory Physics: Foundations of Manufacturing Management, 2nd (ed.), Irwin McGraw Hill, New York, NY.