Although both platforms have many versions of operating systems to consider, Android phones can have many different types of processors, and it can be difficult to optimize an app for all of them. Another issue that can be difficult to work with is screen size. On iOS, developers only deal with a few sizes of iPhone or iPad, but with Android they have to accommodate almost every possible screen size. This makes app development difficult, as they have to find a suitable ratio to scale everything to. Some engines like Unity do this automatically, but if a developer is programming an app from scratch, they will be required to implement these features manually. There are also developers who, once paid, will port an iOS game to Android for the developer. Android phones or tablets may not even have a gyroscope or camera, which can make it impossible to use several games or apps. By notifying users in the app description, developers can ensure that users playing the game have the proper hardware needed to use the app.