I have a series of input fields that are all bound to properties on an AngularJS model that are all editable.

Some of the fields are optionally calculated fields based on the other user input, a sample of the kind of input I'm working with can be found [here](http://jsbin.com/ONOZOQAQ/1/edit).

Basically if someone enters a value in the `time` and `distance` it should automatically work out `speed`, or `speed` and `distance` will work out time, and so on.