In the Outside-In tracking method, base-stations are placed in stationary locations in the environment to track the position of sensors on the tracked device, such as a head-mounted display or controllers. Having multiple base-stations allows for different views of the same markers, and this overlap allows for accurate readings of the device position. Valve’s SteamVR™ Tracking utilizes this technique, placing a constellation of photodiodes on its headset and controllers to allow base-stations in the environment to track their positions. This method is the most mature, having applications not only in VR but also in motion capture technology for film.