Hi,
I suggest that you turn on more logging as described on the wiki - then observe the two values priority and weight and how they change with different settings.
Weight is the value that is used for sorting the queue. In Absolute mode the priority and the weight will be the same but this is not true for fair queueing where each priority is treated as a "bucket", the algorithm will try to distribute resources evenly over the different buckets/priorities.
This basically means that, given that we have three priorities, the sorter will run one jobs from priority one, then one job from priority two, then one from priority three, repeat from priority one.
In weighted mode it will give more resources to higher priorities so that it will (not really but almost), run three jobs from priority one, then two jobs from priority two, then one job from priority three, repeat from priority one.
In both cases the ordering within each bucket will be in the natural order, i.e in the order the jobs enter the queue.
Regards,
/Magnus