The ex stands for "Excellent" where 80% of the overall total marks are gained, and that also means the minimum marks in each secti0n :)

Competitors in WT gain marks, rather than lose them, and there are 5 Stakes altogether, which are the CD, the UD, the WD (Working Dog), TD (Tracker Dog) and PD (Patrol Dog). All involve tracking except for the CD Stake.
Just to give you an idea, for the CD, there is the Control section, which involves heel on and off lead, recall, and Sendaway (often to a hedge, uphill, through fields....although it may be to a tree or a pylon or something!)
Heel on lead gains 5 marks max, off lead 10 max, recall 5 max, and Sendaway 10 max, so a total of 30 for this section. The minimum mark for qualifying is 21.
Stays is the next section, sit 2 minutes and down 10 minutes, handler out of sight.
Agility section - Clear jump, long jump, and the scale which is 6ft (but reduced for smaller dogs, we have a CKCS in our group!!! :p) and this involves a Wait and a Return.
The NOsework section - retrieve a dumbbell, and an elementary search.
Later Stakes involve steadiness to gunshot, tracking, speak under control and also the Patrol Dog involves pursuit and the detention of a "criminal" :D
It's one of the lessser known dog sports but wellworth taking up if you are thinking of doing so..... :)
Lindsay