Jury Scoring

I dont quite understand why it is just a 9 or a 10? Yesterday was the rare case where in the last perfornace on jury member awarded a 8... Its always either a 10 or a 9 if they dont like it... As a result, 4 or 5 contestants end up getting a 100% and in the others, theres not much of a difference either... A chartbuster should really be a thing to achieve and be given to a special performance... I also agree that Shaan said for Picosa that she has got chartbusters in the past but this was her best performance though not a chartbuster...