This displays the level in the document hierarchy. Value 1 corresponds to the selected document, value 2 to the document directly linked to the selected document, 15 being the maximum value of a multi-level log.
Example of a sales invoice with an upstream traceability:
Level 1 = invoice level.
Level 2 = delivery level.
Level 3 = order level.
Level 4 = quote level.
The same level can be used as often as there are levels for this invoice. For instance, there will be a delivery level as often as there are deliveries for this invoice.