I' m thinking that 98 redlines picture is a bit more accurate. An offset does cause the arrow to rotate, but not as much as a helical. It is done by using a straight clamp that is offset from the top of the fletch to the bottom, either right or left. I have found it much easier to use an offset when using vanes as opposed helical. You can use a helical with the vanes, however there is a tendency for the vanes to go back to original straightness (before the glue dries). Feathers are usually put on with a helical instead of an offset for the same reasons. Unless you can find straight feathers.