Reference

1. http://muhamadjaelani35.blogspot.co.id/2013/04/pengertian-interface.html
2. https://adekdik.wordpress.com/2010/04/23/percantik-form-di-vb-net/
3. http://utamibiran.blogspot.co.id/2015/11/interface-pada-sim.html
4. http://informasi-sim.blogspot.co.id/2010/04/konsep-sistem-informasi-manajemen-sim.html
5. https://developer.android.com/guide/topics/ui
6. https://www.webopedia.com/TERM/U/user_interface.html
7. https://en.wikibooks.org/wiki/A-level_Computing/CIE/Computer_systems,_communications_and_software/System_software/User_interfaces
8. https://www.geeksforgeeks.org/software-engineering-user-interface-design/