半档又叫慢档，或者爬坡档。 主要应用在重型货车上，当重载且道路条件不佳，比如泥泞或者爬坡时，半档就发挥作用了，它能降速增距，就是向前的牵引力增大，提高重载车在较差路况的通过性。 半档的速比在所有档位里面最大，故牵引力最强。
2009年晚间10点档节目的电视网络收视率只有五年前的一半。
In 2009 key demographic group ratings for network 10 P.M.shows were just half of what they had been five years earlier.
2009年晚间10点档的电视网络收视率只有五年前的一半。
In 2009 key demographic group ratings for network 10 P.M. shows were just half of what they had been five years earlier.
每一档数字都是比前档减少一半的通孔大小。
Each aperture size (referred to as a stop) is marked with a corresponding number that represents half the light of the previous stop.
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