smooth and consistent surface, which is generally preferred for serious competition. Electrical equipment Power for most slot car tracks comes from a power pack. Power packs contain a transformer, which reduces high voltage house current to a safe 12 to 20V, depending on car type) and usually a rectifier, which changes AC to DC, for cooler running and simpler motors. High-capacity lead-acid batteries are sometimes used for hobby slot cars. Toy race sets may use dry cell batteries at 3 to 6 volts. Controllers ("throttles") vary car speed by modulating the voltage from the power pack. They are usually hand-held and attached by wires to the track. Besides speed control, modern racing controllers usually feature an adjustable "brake", "coast", and "dial-out". Braking works by temporarily connecting the rails together by a switch (or via a resistor for reduced braking); this converts the car's motor into a generator, and the magnetic forces that turned the motor are now slowing it down. Coast allows a certain amount of power to continue to the track after the driver has "let-off" (which would otherwise cut all power to the car). A dial-out allows the driver to limit the maximum power that can reach the car. The early rail-car tracks used telegraph keys, model-train rheostats and other improvised means to control car speed. The first commercial race sets (1957) used handheld controllers with a thumb-button; like the telegraph key, these were either on or off, requiring the driver to "blip" the throttle for intermediate speeds. Later versions had an intermediate speed, and one late version used a buzzer mechanism to provide full-range speed control. From 1959 to about 1965, most HO slot sets had a table-mounted controller with a miniature steering wheel or simple dial-knob operating a rheostat (variable resistor), which gave precise control throughout the car's speed range. This type could be left on a particular speed setting, making it very suitable for model highway layouts, but they were awkward for racing. Around 1960, handheld rheostats began to appear. Most early examples had vertical, thumb-operated plungers with the rheostat in the grip. Aurora had a plunger design in which a stack of carbon/silicon discs replaced the rheostat. Less common styles included a horizontal thumb-plunger and a full-grip squeeze controller. In 1965, Russkit introduced the trigger-operated pistol grip controller. The pistol grip quickly became the standard rheostat-controller style both for race sets and serious hobbyists,