Need help: SAP B1 [Edit Print Layout] with [system variable]

Hi,

I need help with SAP 2007 Bussiness One's system-variable for the "Edit Print Layout" of the 'AP CHECK'.

I have a label field that needs to to be able to dynamcially display data from the Database

depending on the datatype.

Here is my situation:

My "AP CHECK" have line-items and each line-item can either be a [Credit-Memo] or [Invoice].

I need to know how I can display each line-item data using one label field (variable)

Many Thanks,

Tim L.