How do x of marksmanship/swordsmanship/blood magic (+1 while using x) work?

You know those things that give you this 10-20% chance of boosting some attribute by 1 while doing something? How do those work? Do they boost your thing for the rest of the match? Could someone just explain the whole thing? Thanks!

when ever you use a skill of that type.

for example:
you have the +1 marksmanship (chance 20%)
you use powershot, at 16 marksmanship
the +1 marksmanship comes in
you actually get a lvl 17 marksmanship power shot



hope that answers your question!

Thanks, but that seems almost as useful as a sundering string -_-. Ah oh well thanks anyway