Book Reviews

Inventory Control And Management

By C.D.J. Waters

Reviewed by Steve Buchwald, CIRM

I found an interesting article in APICS-The Performance Advantage, about inventory control. The reason I thought it was interesting was that it included some equations that had nine different variables. Now for me, a non mathematical, non inventory control person, this type of article loses me from the get go. So I asked myself if it was possible to address the subject of inventory control or even the subject of the planning and/or buying role without an exhausting discussion of mathematics.

This question was still on my mind when I read a review where the reviewer's perspective was that a good book on inventory control or any of its related functions should not be laden with math. Therefore, I continued to struggle with this question. I decided then that this must be a topic of interest to others and so I decided to see if I could answer that question by reading this book. I chose it because in the preface the author writes, "Because [this book] is aimed at a wide audience, the level of mathematics is kept deliberately low."

Now that I have read this book I am really in a quandary. Almost every page in the book had a mathematical discussion of some sort. So I'm not sure anymore what a low amount of math means in terms of an inventory control discussion. However, if this book is any indication, you P&IC people should be commended on your appetite and tolerance for the complex and the confusing. What I found most provocative about this book is its attempt to reduce to equations the most inexact science of forecasting. For me the best forecast is the non forecast. If a manufacturing concern can keep his promise to ship lead-time less than his total cycle time for obtaining the majority of his raw materials, for manufacturing the product, and for shipping the product, then he will completely eliminate the need for finished good forecasting, and will only have to forecast the estimated usage of those raw materials which have a lead time outside of the lead-time for the majority of his raw material. This seems to me to be common sense and very simple and if I understand JIT at all is the basis of the JIT philosophy as it relates to Inventory Control (Reduce the cycle time to reduce the buffer stocks and the lumps in demand that cause inventory).

Nonetheless, I do realize that this is not always possible, and that forecasting may be a necessary evil. To this point, I will say that this book did cover all the subjects quite thoroughly. What still troubles me is that it appears that the math detracts from and does not add to the discussions. Furthermore, with the power of today's computers do we really need to understand and apply the mathematics. Aren't we in a position now where we can understand the constraints and relay these messages to the computer software to do the number crunching. I'm not involved in this type of work day in and day out so I'm throwing this out for discussion. The book will be available for review and we can discuss whether or not you believe the math adds to or detracts from the real message.

One final comment is that this book is really a text book and you really can't read a text book all at once, you need to put it on the shelf and use it for reference. For this purpose, I believe the book could be quite effective and I'm sure that there are some practitioners or educators who can really get a lot out of this book using it this way. However, based on the preface I don't think this was the authors intent.

Good reading!