This application has a widget that displays the exchange rate between two currencies.
The widget can be added to the android home screen by searching for it in the widgets section of the phone launcher application.
The application also has a window for selecting the source and target currency.
The value is updated periodically but also has the option to update manually, both from the configuration application and from the widget itself.
Tapping once on the widget will display the option to update and view the configuration window, these options disappear if the widget is tapped again.
The widget adjusts to different sizes, as desired by the user.