σ is a Greek letter, sigma in English and Sigma in Chinese. The term σ is used to describe the distribution or dispersion of the average value of any process parameter.

The meaning of σ applies to business or manufacturing process.

For business or manufacturing process, σ value is a measure to indicate the working condition of the process. The higher the σ value, the better the process conditions. σ value is used to measure the ability of the process to complete defect-free operation, because defects will lead to customer dissatisfaction in any case. In other words, the σ value indicates the frequency of defects, and the higher the σ value; The lower the process defect rate. When the σ value increases, the defective rate decreases, the quality cost decreases, the process cycle time shortens, and the customer satisfaction improves. When the σ value reaches 6, that is, the quality of 6σ means "only 3.4 defective units per million", and the long-term quality compliance rate is 99.99966%. Relatively speaking, when the σ value is only 3, that is, the quality of 3σ means "there are 66,807 defective products per million units", and the qualified rate is 93.32%.

Chemically, surface tension (σ)(sigma) refers to the force that molecules on the surface of a liquid shrink inward to the smallest area.

Chemically, it also refers to the σ bond formed by two electron clouds "head to head" along the orbital axis.

For average sum and stability, there must be a specific mathematical value to quantify its stability or not. σ is a specific mathematical value used to quantify the degree of stability and instability, which is itself a concept of error analysis in statistics. It is borrowed here to indicate the quality. When applied to enterprise management, σ represents the standard deviation, and the smaller the σ value, the more stable the label quality level; On the contrary, the greater the σ value, the more unstable the quality level is. If a company needs a stable process, it should try its best to reduce the σ value. Statistically speaking, σ value is a measure of process, and the specific calculation of σ value will be explained in the course of green belt and black belt in the future. Every result is produced by a process. The process is repeated, but there will be some subtle differences in the output of the process, which is called fluctuation. Only by controlling the difference of these outputs and making them change within a reasonable range can the quality of products be guaranteed. Fluctuation is also called dispersion degree. Due to the difference of dispersion and concentration, fluctuation is the standard measure of process quality. In the past, the average value was used to measure the quality of the process, but now σ is added to measure the degree of dispersion and concentration. In this way, the process can be evaluated more ideally and comprehensively.

In HPLC, σ refers to the standard deviation, which is half the peak width (inflection point) of chromatographic normal distribution curve x = 1. The inflection point of normal peak width is 0.607 times of peak height. The standard deviation indicates the dispersion of components in the process of flowing out of the chromatographic column. Small σ, small dispersion, high polar concentration, fine peak shape and high column efficiency; On the contrary, σ is large, the peak shape is fat and the column efficiency is low.

6σ

This concept was put forward by blll smith of Motorola in 1986, which belongs to the category of quality management. Sigma (σ, σ) is a Greek letter, which is a unit in statistics and represents the standard deviation from the average. The purpose is to reduce the number of defects in products and processes, prevent product variation and improve quality. The origin of six suitable horses

Six Sigma is an efficient enterprise process design, improvement and optimization technology, which evolved from the total quality management method proposed by GE in the mid-1990s, and provided a series of new product development tools that are also suitable for design, production and service. Then keep pace with GE's globalization, service, e-commerce and other strategies, and become the most important strategic move for enterprises pursuing excellent management in the world. Six Sigma has gradually developed into a management concept of taking customers as the main body to determine the strategic objectives of enterprise and product development and design, and pursuing continuous progress.

Six Sigma Management, which was developed in 1990s, summed up the successful experience of total quality management, refined the essence of process management skills and the most effective methods, and became a management model to improve enterprise performance and competitiveness. This management method has been proved to be effective in many multinational enterprises such as Motorola, General Motors, Dell, Hewlett-Packard, Siemens, Sony and Toshiba Bank. To this end, some domestic departments and institutions vigorously promote 6σ management in domestic enterprises and guide enterprises to carry out 6σ management. For example, the probability of 6σ in general process capability is 99.73%.

The 6 sigma system originated from Motorola has become one of the milestones in the development of quality management. The 6 sigma system has gradually expanded from the improvement of manufacturing links to the reengineering of almost all business processes, from Whirlpool, GE, LG, Dell Computer, DHL Logistics, Dow Chemical, DuPont, Agilent Pharmaceutical, GSK, Vodafone Communication, Tel Korea, BoA Finance, Merrill Lynch and HSBC to the US Army, Navy and Air Force.

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