MarkRHamel's blog

Changeover Time

Changeover time represents the elapsed time to changeover from the production/processing of one product or service to a different product or service. Admittedly, there is little math involved here. Some readers may scratch their heads and wonder why one would need a math entry at all! However, changeover time is important in the overall scheme of Lean Math and, with it, the principle of flow and pull. More specifically, internal changeover time (T∆i) is a critical driver of batch sizes, lead time, and intervals.

Pitch interval (Ip) can be thought of in two ways: 1) as a unit of time representing the (usually) smallest common pitch shared among a range of products, services, or transactions that are being produced, conveyed, performed, or executed by a given resource(s), and 2) as a count of the number of intervals of a common pitch over a period of time, typically a shift or day.

It all started when my colleague and I noted that we had used the same data to calculate Cpk, but ended up with different results. This led us down an Alice in Wonderland-like path of Google searching, Wikipedia reading, and blogosphere scanning. After several days of investigation, we determined that there was no consensus on how to properly calculate estimated standard deviation. Knowing that there must be a misunderstanding and that this should be purely an effort based on science, we decided to get to the bottom of this.


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