What determines a table’s sort order?

Index field determines a table's sort order

In this example, you can see that the entry date is not in date order. Neither are the entries in columns C, D and E. By contrast, the Income column is determining the order. It goes from low to highest. This is the index field. It may be that another determinant could be chosen for the Index field, such as number sold. The essence is that the index field is the area of interest; i.e. what the data output is to show.