A key requirement in a Lean operation is to make abnormal conditions stand out. Obviously, to recognize abnormal, you must also understand what normal is. Nominal conditions define your standard and let you see that you are operating within acceptable limits. Note that the term “nominal conditions” is not one that is in common use in the Lean community. Regardless, it is an important concept.
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The first key to knowing if something is operating within acceptable limits is to establish what acceptable limits are. Most production environments put this concept to relatively frequent use. They have a production plan, and know how much product should be produced. The machinery used in production processes has gauges that show optimum operating conditions. These are even frequently highlighted so the nominal range stands out.
Unfortunately though, many administrative processes are not as clear in defining what “normal” looks like. There nominal conditions are undefined. For example, an HR representative contacting candidates may not know how many phone calls should be placed per hour. Without an understanding of the typical pace, the rep would be hard-pressed to decide if an abnormal condition existed, and if he or she needed help. Likewise, the number of emails in an inbox or the number of projects in a queue are also seldom compared to a standard.
The second key to defining nominal conditions is to be able to measure in the moment (in-process metrics). That is, in many cases, relatively simple to do in manufacturing. You might not really be able to measure production exactly in the moment, but you can get pretty close. You may know that at 12:00, you should have 6 products completed. If you are behind, you know you are outside your nominal conditions. Of course, the closer you can get to real-time measurement, the better. Lagging indicators are far harder to use to make decisions. Think of it like driving a car by looking through the rearview mirror. By the time you notice your wheels are over the white lines, it is often too late to make an adjustment. It is far better to be able to act the moment something falls outside of nominal conditions.