Seven-segment display letter to be unambiguous, merely for the words as a whole to be readable. Similar displays with fourteen or sixteen segments are available allowing less-ambiguous representations of the alphabet. Using a restricted range of letters that look like (upside-down) digits, seven-segment displays are commonly used by school children to form words and phrases using a technique known as "calculator spelling". Seven-segment display A seven-segment display (SSD), or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays. Seven-segment displays are widely used in digital clocks, electronic
Sixteen Prefectures Ji County in modern-day Tianjin Municipality to Datong in Shanxi Province, extending contiguously along the mountains that divide the agrarian plains of central China from the pastoralist steppes to the north. Several dynasties including the Qin and the Northern Dynasties before the Tang built the Great Wall along these mountains. Seven of the Sixteen Prefectures were located inside (south) of the Inner Great Wall. The other eleven were located in between the Inner and Outer Great Walls. The Tang did not build Great Walls but used frontier military commanders to guard against the northern tribes. The Fanyang or Youzhou-Jizhou Commandery,