3 sentences

1. 古人通过圭表投下的影子来确定冬至和夏至。

   gǔ​rén tōng​guò guī biǎo tóu​xià de yǐng​zi lái què​dìng Dōng​zhì hé Xià​zhì.

   The ancients determined the winter and summer solstices by observing the shadows cast by the gnomon.

   Source: Dong Chinese Dictionary

2. 他做事严谨，哪怕是一圭一铢的误差都要纠正。

   tā zuò​shì yán​jǐn, nǎ​pà shì yī guī yī zhū de wù​chā dōu yào jiū​zhèng.

   He is very meticulous and corrects even the slightest error.

   Source: Dong Chinese Dictionary

3. 在古代仪式中，公爵朝见天子时通常需要手持青圭。

   zài gǔ​dài yí​shì zhōng, gōng​jué cháo​jiàn tiān​zǐ shí tōng​cháng xū​yào shǒu​chí qīng guī.

   In ancient ceremonies, dukes usually had to hold a green jade tablet when meeting the Emperor.

   Source: Dong Chinese Dictionary