You've probably heard about the "incumbent" rule. It states that undecided votes
in a poll tend to go heavily for the challenger. This tool is meant to compute the final
vote with this "sway" taken into consideration.
One blog (MyDD) computed that for a presedential race, the
sway is 85% in favor of the challenger. This page will take a poll result and
predict what the final vote will be.
Next, many believe that the pollsters are missing certain blocks
of voters. For example, cell phone users, college students, etc. Most data I
have seen says that these voters will break for Kerry by around 58% or more.
So, if Kerry is not winning from the original poll numbers, this will compute the amount
of new voters that are needed to push Kerry into the "win" column. You can change
the new voter sway percentage by adjusting this value.