All legal and natural persons (entrepreneur) are obliged to issue a tax document when goods or services are delivered. An example is an invoice as a document to which a debit note (or a correction of an invoice issued) refers. It is marked with a “+”, indicating an increase in a receivable charged in advance. A debit note arises in the event of an increase in the unit price, overtime or incorrectly estimated data regarding work. On the other hand, if the price or quantity represents a decrease and a negative value, a credit note must be issued.