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A number range is a sequence of numbers with a start and an end. It also contains the current number that is being used. For example, when a sales document of type OR is being created, the number range lies between 1 and 199999. Also it is defined as an internal number range. So when a new sales order is being created, the user does not enter the sales order number when saving. Instead SAP automatically generates a sales order number in the system for our reference.
Number ranges have two purposes.
Document Number range means
You assign one or more document types to each number range. The number range becomes effective via the document type specified in document entry and posting. You can use one number range for several document types. This means you can differentiate documents by document type but combine them again for filing the original documents, provided you store your original documents under the EDP document number.