Field help (ARCCATEG) 

This field contains an evaluated formula where the result is used to load the 'category' heading in the attachment, when an attachment is created on archiving the document. This is a numeric value defined by the local menu 96.

This is a calculation formula using all the variables likely to exist in the context (this depends on the triggering event) and especially the G_XXXX variables where XXXX is the code of a setup passed in an argument in the Variable tab.