In Angular, how tow arrays can be changed in one $digest loop?

In the answer to Databinding in angularjs, @misko-hevery mentioned

'Suppose you have two arrays which need to be kept in sync for whatever reason, ...'.

I have a simliar problem. Say I have two arrays: knives and forks. I want to change them and fire only one event and update the UI only once. The sample code is here(http://jsbin.com/efolag/3/edit).

I copied the javascript code here:

var app = angular.module('app',[]);

function Main($scope){
  console.log("initialize controller Main");
  $scope.value="a";
  $scope.$watch("newItem",function(newValue){
    $scope.knives=["a","b","c", newValue];
    $scope.forks=["d","e","f", newValue];
  });
}

My question is how many dirty checking loops will the changes to knives and forks trigger? If it is more than once, is it possible to make it fire only once?