If an attack has the radius spc.rule and a miss is rolled, times your roll (without any modifiers) by D3. this is the amount that the center of the radius moves in the direction indicated below:
3moves to the right
4moves to the left
If any models are under the radius at all, even if they aren't from the same unit or side, the they suffer the appropriate amount of damage. Two examples of how this works follow:
A rum gun fires on a unit troopers, but rolled a 3 on the to hit roll. They then a roll 2 followed by a 5 which means that the center of the radius moves 6 inches backwards; and accidental hits 2 goblins.
A terrpeda battaefires its terrpeda at a unit of vinelings, but rolled a 1. They then rolled a 3, but this was followed by a 6, so the shot completely missed (or more likely, blew up in the air).