The diagram depicts the stages of manufacturing and process adjustment of the customer goods.

The diagram depicts the stages of manufacturing and process adjustment of the customer goods. It is noticeable that the good manufacturing is complex procedure which is done in several steps and information feedback is given to earlier stages to allow for adjustment.

Firstly, raw materials and manufactured components are stored together, before through to the production planning, there are two major processes involving product research and design. After both of the stages are already done, the input is used in product planning process. Next, assembly process depends on the previous stage where it is determined how and how much quantities the stored materials will be processed to produce finished goods. Following this, the products are tested and checked to maintain quality control in which if the good are free from defects, it will directly to be packaged and dispatched. After that, products are ready to be spread over retail outlets. Sales are the end of manufacturing process, and it supports production planning to distinguish the product is it good or bad.

Feedback from testing phase is used in controlling inappropriate problems in finishing product. Then, adjustments will have to be created to the design stages. Following this, market research is used in order to observe trend in market and to examine the demand for product which is designed to be suitable for costumers. Market research, which has a functional to encourage the stabilization of product sales by planning appropriate advertising for the goods

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I see that you use 'the' sometimes when it's not needed. Your Engish is almost perfect, wth just a few areas for improvement.

...adjustment of the customer goods. It is noticeable that the good manufacturing is complex procedure ...

.... and information feedback is given to earlier stages to allow for adjustment. --- This part is very good.

And here is a place where 'the' is necessary but you did not use it:
... the input is used in the product planning process.

The only way to improve your sense of when to use the article 'the' is to read often, and perhaps even read aloud to program your brain with the correct habits.

Next, the assembly process ...

Your writing style is excellent, and with just a bit more practice I think it will be perfect. : )