1) Lit: ''Like an egg'' - 57.6 cc.according to Shiurei Torah, 100 cc. according to the Chazon Ish. 2) Revi'it - 3.2 - 4.42 fluid ounces depending on which authority you follow. 3) The Shulchan Aruch HaRav (273) rules that in time of need, one can rely on drinking only a Revi'it rather than a Revi'it and a cheek-full. 4) Lit: ''like an olive''. 5) Wheat, Barley, Spelt, Oats and Rye.

1) This obligation is based on the repetition of the word ''HaYom'' (today) three times in a verse which quotes Moshe telling the Nation to eat the Manna on Shabbat: ''And Moshe said: Eat it today, for today is Shabbat before Hashem, today you will not find it in the field'' (Exodus 16:25). There is a dispute among the authorities as to whether this is a Biblical or Rabbinic obligation (probably based on the dispute as to whether the mitzvah of ''Oneg Shabbat'' (physical pleasure on Shabbat) is Biblical or Rabbinic in nature). 2) The Sages of the Talmud taught that one who fulfills the Mitzvah to eat three meals on Shabbat will be spared three types of retribution: the tribulations preceding the coming of the Messiah, the judgement of Gehinom (the Jewish understanding of ''Hell''), and the apocalyptic war between Gog and Magog (Tractate Shabbat 118). 3) There is a dispute among the authorities as to whether the obligation to eat bread for the Shabbat meal is Biblical or Rabbinic. 4) Lit: ''like (the size) of an egg''. See also Chapter 40, Law 1. The Mishna Berurah (291:2) writes that one should eat a little more than a ''K'beitzah'', because eating exactly a ''K'beitzah'' is considered a snack, not a meal. However, if eating more than a ''K'beitzah'' is not possible, one can fulfill one's obligation with a minimum of a ''K'zayit'' (lit: ''like (the size of an) olive). (5) Wheat, Barley, Spelt, Oats and Rye. 6) In such a case, the cake is treated with all the halachic requirements of bread, that is, washing with the blessing on the washing of the hands'', blessing ''who brings forth bread'' over the cake, and saying Grace after the meal. 8) ''Seasonal hours after sunrise. A ''seasonal hour'' is equal to one twelfth of the time from sunrise to sunset (some say from dawn to dark) See Rema 261:2.

כל אדם מישראל בין איש או אשה חייבים לאכול בשבת שלש סעודות אחת בלילה ושתים ביום וחייב לאכול בכל סעודה פת ואפילו בסעודה שלישית יזהר מאד לאכול פת דוקא וכיון שהוא נוטל ידיו ומברך על הנטילה צריך לאכול פת כביצה לכן יזהר כל אדם שלא למלאות כרסו בסעודת שחרית כדי שיוכל לקיים מצות שלש סעודות ואם אי אפשר לו כלל לאכול פת גמור יאכל לכל הפחות פת כיסנין או שאר מאכל העשוי מחמשת מיני דגן שמברכין עליו בורא מיני מזונות שהוא נקרא מזון ואם גם זאת אי אפשר לו יאכל על על פנים דברים שדרך ללפת בהם את הפת כגון בשר ודגים וכיוצא בהם ואם גם זאת אי אפשר לו יאכל על כל פנים פירות מבושלים זמן סעודה שלישית היא משיגיע זמן מנחה גדולה דהיינו משש שעות ומחצה ואילך

1) The source for this is the verse in the Torah which states that the Jews would collect ''Lechem Mishna'' (double portion) of Manna on Fridays, because no Manna would fall on Shabbat. As a remembrance of this double portion, we begin each Shabbat meal with two loaves. There is a dispute among authorities as to whether this obligation of having two loaves is Biblical or Rabbinic. 2) A loaf is considered whole even if there is a split or crack, provided that when one lifts the loaf by the weaker section, it does not break in two. Two loaves that have become attached during baking, are still considered whole when separated. A partially burnt loaf is still considered whole. 3) So as to minimize the delay between the blessing and the actual eating of the bread. 4) According to the Shulchan Aruch 274:1 one should place one loaf on top of the other and hold them in one's hands while making the blessing. Based on Kabbalistic sources, the Shulchan Aruch and Rema write that on Friday night, one should cut first from the bottom loaf, whereas on Shabbat day one should cut the upper loaf first. There is a principle in Jewish law called ''Eyn Ma'avirin Al HaMitzvot'' (One shouldn't pass over Mitzvot) which says that when one has two or more objects in front of him with which he will be performing a Mitzvah, one should arrange them in such a way so that one won't have to reach over one, or move one aside, in order to get to another. Therefore, regarding the Challah on Shabbat, since one is supposed to cut the bottom Challah first, one should hold it a little closer to one's body than the top Challah. 5) The Maharsham (289) disagrees because he holds that if one does this, it will indicate that one is having a regular meal, and one will be obliged to wash, say ''who brings forth bread'' and then Grace after the meal. The custom follows the Maharsham. However, if one does not have bread for the main meal, one may fulfill one's obligation of ''Lechem Mishna'' (Two loaves) with two whole cakes or pastries. In that case, all laws applying to bread would apply to the cake.