While both platforms have many operating system (OS) versions to consider, Android phones can have many different processor types, and it can be difficult to optimize an application for each of them. Another issue that can be tricky to resolve is screen size. On iOS, developers only support a few iPhone or iPad sizes, but with Android, they have to accommodate almost every possible screen size. This makes app development difficult, as they need to find a suitable ratio to scale everything. Some engines like Unity do this automatically, but if a developer programs an application from scratch, they will have 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 also not have a gyroscope or camera, which may make it impossible to use multiple games or apps. By notifying users in the app description, developers can be sure that users playing the game have the appropriate hardware to use the app.