and sent the resulting data to other ships in a task force using pulse-code modulation radio signals. DATAR's trackball used four disks to pick up motion, two each for the X and Y directions. Several additional rollers provided mechanical support. When the ball was rolled, the pickup discs spun and contacts on their outer rim made periodic contact with wires, producing pulses of output with each movement of the ball. By counting the pulses, the physical movement of the ball could be determined. Since 1966, the American company Orbit Instrument Corporation produced a device named X-Y Ball Tracker, a trackball, which was embedded into radar flight control desks. A similar trackball device at the German was constructed by a team around of Telefunken as part of the development for the Telefunken computer infrastructure around the main frame , process computer TR 86 and video terminal SIG 100-86, which began in 1965. This trackball was called (German for "rolling ball"). Somewhat later, the idea of "reversing" this device led to the introduction of the first computer ball mouse (still named , model RKS 100-86), which was offered as an alternative input device to light pens and trackballs for Telefunken's computer systems since 1968. In later trackball models the electrical contacts were replaced by a "chopper wheel" which had small slots cut into it in the same locations as the contacts. An LED shone light through the slots to an optical sensor, As the disk rotated the slots alternately lined up and then blocked the light from the LED, causing pulses to be produced in the sensor. The operation was otherwise similar. Mice used the same basic system for determining motion, but had the problem that the ball was in contact with the desk or mousepad. In order to provide smooth motion the balls were often covered with an anti-slip surface treatment, which was, by design, sticky. Rolling the mouse tended to pick up any dirt and drag it into the system where it would clog the chopper wheels, demanding cleanup. In contrast the trackball is in contact only with the user's hand, which tends to be cleaner. In the late 1990s both mice and trackballs began using direct optical tracking which follows dots on the ball, avoiding the need for anti-slip surface treatment. As with modern mice, most trackballs now have an auxiliary device primarily intended for scrolling. Some have a