Comment by fluoridation

How is the table of dialects constructed? It's obvious if two dialects are at 1, but what does it mean if they're at 0? They can't be mutually unintelligible, since that would make them different languages. I ask because the dialects spoken in Argentina and in Uruguay are practically identical, save for a few regional words. If the scale being used puts them at 0.35, then it makes me wonder about the usefulness of the scale.