A central Database needs to be build. There all the Parameters should be stored. Those parameters include Items, Prices, Staff Names, Customer Names (taken from another database), a table for all sales (every sale should be recorded in one table). Then four different forms should allow sales (they are all similar but not completely the same) for different locations. These Sales Forms should use the parameters that are stored in the main Database and should again store sales in the main database.
Also there needs a form that allows to create invoices. On the invoices all (open) sales to a specific customer should be shown and grouped (if a customer buys two of the same items on different times there should not be 2 lines on the invoice but 1 line with the quantity 2) Once an invoice has been created it needs to be "posted" and at the same time all sales data should have a invoice number assigned. So that they will not show when an invoice is produced for the next time.
Furthermore there need to be some reports for stock.
A precise description of all needed forms, tables and reports can be viewed in an excel table that I will send in the next project step.