semi-automatic transmissions are based on conventional manual transmissions, but are usually operated with an automatic clutch or another kind of partially automated transmission mechanism. Once the clutch becomes automated, the transmission becomes semi-automatic. However, these systems still require manual gear selection by the driver. This type of transmission is called a clutchless manual or an automated manual. Most semi-automatic transmissions in older passenger cars retain the normal H-pattern shifter of a manual transmission; similarly, semi-automatic transmissions on older motorcycles retain the conventional foot-shift lever, as on a motorcycle with a fully manual transmission. However, semi-automatics systems in newer motorcycles, racing cars, and other types of vehicles often use gear selection methods such as shift paddles near the steering wheel or triggers near the handlebars. Several different forms of automation for clutch actuation have been used over the years, from hydraulic, pneumatic, and electromechanical clutches to vacuum-operated, electromagnetic, and even centrifugal clutches. Fluid couplings (most commonly and formerly used in early automatic transmissions) have also been used by various manufacturers, usually alongside some form of mechanical friction clutch, to prevent the vehicle from stalling when coming to a standstill or at idle. A typical semi-automatic transmission design may work by using Hall effect sensors or micro switches to detect the direction of the requested shift when the gear stick is used. These sensors' output, combined with the output from a sensor connected to the gearbox which measures its current speed and gear, is fed into a transmission control unit, electronic control unit, engine control unit, or microprocessor, or another type of electronic control system. This control system then determines the optimal timing and torque required for smooth clutch engagement. The electronic control unit powers an actuator, which engages and disengages the clutch in a smooth manner. In some cases, the clutch is actuated by a servomotor coupled to a gear arrangement for a linear actuator, which, via a hydraulic cylinder filled with hydraulic fluid from the braking system, disengages the clutch. In other cases, the internal clutch actuator may be completely electric, where the main clutch actuator is powered by an electric motor or solenoid, or even pneumatic, where the main clutch actuator is a pneumatic actuator that disengages the clutch. A clutchless manual system, named the Autostick, was a semi-automatic transmission introduced by Volkswagen for the 1968 model year. Marketed as the Volkswagen Automatic Stickshift, a conventional three-speed manual transmission