ckor = 1 stands for an inserted orderline, ckor = 2 for a cancelled orderline and ckor = 3 is a processed (session process delivered salesorders) or invoiced orderline.
In case a salesorderline is changed by a user, Baan generates a "negative" entry in order to "cancel" the entry with the old value(s). This is a record with ckor = 1 and sern = 0. At the same time a second record is generated with ckor = 1 and sern = 1 and the new value(s) for the changed field(s) in tdsls041. Ok so far?
Just a simple example:
ckor sern itemcode quantity
Newly entered salesoderline : 1 0 X 1
change itemcode from X to Y : 1 0 X -1
1 1 Y 1
Hope that helps.