From [here](https://docs.angularjs.org/guide/controller)

> 
> In general, a Controller shouldn't try to do too much. It should
>  contain only the business logic needed for a single view.
> 
> 
> 

I can't understand why it's controller. It must be model. Please,explain.

EDIT:  

This is the example from official developer guider:

```
angular.module('invoice1', [])
.controller('InvoiceController', function() {
  this.qty = 1;
  this.cost = 2;
  this.inCurr = 'EUR';
  this.currencies = ['USD', 'EUR', 'CNY'];
});

<div ng-app="invoice1" ng-controller="InvoiceController as invoice">
  <b>Invoice:</b>
  <div>
    Quantity: <input type="number" min="0" ng-model="invoice.qty" required >
  </div>
  <div>
    Costs: <input type="number" min="0" ng-model="invoice.cost" required >
    <select ng-model="invoice.inCurr">
      <option ng-repeat="c in invoice.currencies">{{c}}</option>
    </select>
  </div>

```

What I don't understand is that controller = model here. Am I not right?