The first hydrostatic transmission (HST) installed on a walk - behind lawn mower was introduced 1989. The HST is tiny and efficient. The HST unit weighs 3.1 kg, has a pump displacement of 2 cm3 and a maximum overall efficiency of 72 percent. Since the driving direction is limited to forward, the hydraulic circuit can be simplified. The hydraulic circuit is integrated to the aluminum die-cast transmission case.Operation of both drive and shift levers are converted to the stroke of one single shift cable. This integral operation mechanism enhances such original HST's characteristics as starting with less shock and smooth shifting. Consequently, operational ease of the mower has been drastically upgraded in various locations, especially on inclined surfaces and narrow areas where this type of mower is frequently used.