What is a Zeres?
Rashi: A Zeres is half an Amah. 1
The distance between the small finger (Zeres) and the thumb that are both extended to their maximum.
What are the connotations of "Ravu'a Yih'yeh Kaful`"?
Rashi: The Choshen, which measured an Amah by half an Amah when manufactured,, was then folded over in front of him, over his heart to measure half an Amah by half an Amah. 1
Da'as Zekenim, Hadar Zekenim: There were two Choshens. The stones were fixed in the outer one; the inner one was stuck to it, lest the stones fixed in the settings get ruined. Toras Kohanim supports this. It says, perhaps just like it is double, also the Efod
Rashbam: It is like a pocket, into which they placed the Urim ve'Tumim (Pasuk 30).
What purpose did the pocket in the Choshen serve?
Why does the Torah not mention them here?
Ramban #1 (on Pasuk 30): The Torah deliberately curtails mention of them due to their mystical connotations. 1
Ramban #2: The Torah only mentions the Urim ve'Tumim when instructing Moshe to place them inside the Choshen. It does not mention them earlier, because, neither the people, nor the craftsmen 2 had a hand in them - neither as regards the donation nor as regards making them. In fact, they were made either by Moshe in sanctity, based on a secret formula of which only Moshe was aware, or by Hashem Himself. 3
Seeing as four letters ('Ches', 'Tes', 'Kuf' and 'Tzadik' do not appear in the names of the twelve tribes, how could the Urim ve'Tumim be guaranteed to answer all the questions that were put to it?
Ba'al ha'Turim (on Pasuk 17, from Yoma 73b): The words 'Avraham, Yitzchak, Ya'akov Shivtei Yeshurun' were added to the names of the tribes. 1
Chizkuni (21), Ba'al ha'Turim: Arranged in the following way, so that each stone contained six letters, making a total of seventy-two (Refer to 28:30:1:1*): Odem: Reuven - 'Alef'; Pitdah: Shimon - 'Beis; Barekes: Levi - 'Resh' 'Hey' 'Mem'; Nofech: Yehudah - 'Yud'; Sapir: Yisachar - 'Tzadik'; Yohalom: Zevulun - 'Ches'; Leshem: Dan - 'Kuf' 'Yud' 'Ayin' Kuf'; Sh'vo: Naftali - 'Beis; Achlamah: Gad -'Shivtei'; Tarshish: Asher - 'Yud' 'Shin' 'Resh'; Shoham: Yosef - 'Vav', Nun; Yoshpeh: Binyamin;
In which order were the names of the tribes engraved on the stones?
Rashi (on Pasuk 21) and Targum Yonasan (Pesukim 17 - 20): It is the order in which they were born 1 - Odem for Reuven
Gur Aryeh (on Pasuk 21): Even though "k'Soldosam" is written only about the Avnei Efod, since it says "Ish Al Shmo", it means in the order proper for them, i.e. the order in which they were born. See also Na'ar Yonasan.