Angular: Empty Fiddle

http://angularjs.org/

HTML

<script src="http://code.angularjs.org/angular-1.0.1.js"></script>
<div ng-controller="MyCtrl">
  <input type="number" step="0.01" ng-model="uf" ng-change="change('uf')"/>
  <input type="number" step="0.01" ng-model="uc" ng-change="change('uc')"/>
</div>

JavaScript

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

function MyCtrl($scope) {
    $scope.coeff = 0.5;
    $scope.uf = "25";
    $scope.uc = "";
    
    $scope.change = function(type) {
        console.log(type, "changes!");
        
        if(type == 'uf') {
            $scope.uc = $scope.uf * $scope.coeff;
        } else if(type == 'uc') {
            $scope.uf = $scope.uc / $scope.coeff;
			  }
    }
}