Martyn Webster

Hah! made the same maths error as the book! 

"...they know that 8 is 8 under 11 + 5 = 16 so they hit DCV 8."

I would like to echo Tygermark's comments about presenting the maths and make the following suggestion:

I think it is worth framing it in a similar way, but the player will often not know the exact DCV of the target. The more "technically aware" player knows their own modified OCV and can say what DCV they hit from "how much they roll under 11 plus their OCV". Eg. if the player OCV is 5 and they roll an 8 (as above), they know that 8 is 9 under 11 + 5 = 16 so they hit DCV 9.

Another way to look at it is that a roll of 8 means you hit 11 - 8 = 3 more DCV than your OCV. if you roll (say) 13, you hit a DCV 2 less than your OCV. This OCV vs DCV difference is a intuitively more familiar factor. The player knows that if they roll low (under 11) they will hit even a tougher target. If over 11, they will only hit an easier target. If they roll 11, they will hit the same DCV as their OCV. It's a lot easier to think of the relative difficulty and know that "low is good, high is bad" and then work out how good or bad which involves smaller numbers.