Making a bar chart whose bars change whenever some underlying numbers change.

[John Baber]

I think I'm not understanding how to use NumericProperty correctly.  It's easy to see what I'd like to do by running this code: https://gist.github.com/jbaber/d13e42e26a58dc45e5f4 I keep changing the scores of the users.  I'd like the bars to change correspondingly.