As with all previous generations of iPhone and iPad hardware, there are four buttons and one switch on the fourth-generation iPad. With the device in its portrait orientation, these are: a "home" button on the face of the device under the display that returns the user to the home screen, a wake/sleep button on the top edge of the device, and two buttons on the upper right side of the device performing volume up/down functions, under which is a switch whose function varies according to device settings, generally functioning either to switch the device into or out of silent mode or to lock/unlock the orientation of the screen. Externally, the fourth-generation iPad is identical to its predecessor apart from the differences between dock connectors used and change of manufacturers that produce the display. In addition, the Wi-Fi only version weighs 652 grams while the cellular model weighs 662 grams – 2 grams heavier than their respective predecessors.  The display responds to other sensors: an ambient light sensor to adjust screen brightness and a 3-axis accelerometer to sense orientation and switch between portrait and landscape modes. Unlike the iPhone and iPod Touch's built-in applications, which work in three orientations (portrait, landscape-left and landscape-right), the iPad's built-in applications support screen rotation in all four orientations, including upside-down. Consequently, the device has no intrinsic "native" orientation; only the relative position of the home button changes.