Show HN: Magic Square App w/ Meteor (magic-square.meteor.com)

I've been messing around with seeing how to make interesting math games online -- this is a simple adaptation of a game I used to play with kids I taught with paper and velcro.

The interesting feature -- that it sums as you work -- only shows up once you start inputting numbers. Feedback, suggestions, and criticism welcome as I'm quite new to building for the web!