there. If things get out of sync, or if the control stick was not centered during power-on, the center position can be reset by pressing the left and right shoulder buttons (L and R) at the same time as the Start button. While the optical encoding disks are mostly digital and provide very accurate relative movements, third party controllers and joysticks often use cheaper potentiometers instead. These allow the controller to track the absolute position of the joystick, but since the signal is analog, it is very noisy and can fluctuate even if the joystick is not moved. Controller Pak The Controller Pak is Nintendo's external memory card, similar to those used on the PlayStation and other CD-ROM consoles. Though the Nintendo 64's cartridges can store battery-backed memory much like its predecessors, in supported games the Controller Pak allows save game data to be stored separately from the cartridge; for instance allowing save data to be used with a different copy of the game, or to store data that will not fit on a cartridge's battery-backed memory (such as Mario Kart 64s ghost data). Whereas other console developers opted to plug the memory card directly into a console, Nintendo opted to have the card be plugged into the controller and thus transported as one unit, envisioning scenarios in which players would want to bring their own controller and memory card to play with other Nintendo 64 owners. In such scenarios having the cartridge port on the controller would allow individual players to each use their own distinct game settings and controller configurations while playing simultaneously on the same system. Rumble Pak The original Rumble Pak, designed for the Nintendo 64 controller, was released in April 1997 to coincide with the release of Star Fox 64 and requires two AAA batteries. It provides haptic feedback during gameplay, intending to make the gaming experience more engaging. It was designed to be inserted into the controller's memory cartridge slot, which prevents the use of the Controller Pak. The insertion of a Controller Pak is prompted at every point of save in case one was not already in place. LodgeNet variant In 1999, LodgeNet and Nintendo released a controller and game playing service for various hotels in the United States. It is a slightly modified Nintendo 64 controller featuring an improved GameCube-style analog control stick, and LodgeNet TV control buttons. It attaches to the