The measurements used in the Torah (cubit, span, hin, and others) are only known approximately. Those used in the Talmud would seem to be more straightforward; the bulk of an olive (k'zayit), the bulk of an egg (k'beitzah), the hand breadth (tefach), the width of a thumb (etzba').) However, this is not the case. How big were the olives then? The eggs? Were the people the same size as we are? This comes into play in many areas of halachah, but is especially important for Passover. There is a Biblical requirement to eat a k'zayit of matzah on the first night of Passover (and the second in the Diaspora by rabbinic law). Moreover, we eat more than one k'zayit; one after the narrative part of the Haggadah (this is the main one), one together with the maror (bitter herb; also requiring a k'zayit), and one after the meal as Afikoman (some say two at this point). Estimates for the k'zyit vary all the way from 6 gm, to 60 gm.! (I go by 10, but most people go by 30, with the 60 gm. measurement standard in "Yeshivish" communities.) That woulod mean from a sixth of a machine matzah, to two whole machine matzot for the k'zayit). The Israeli ambulance service, Magen David Adom, reports their busiest time for calls is on Passover night, with many people chocking on the exaggerated estimates of a k'zayit, exacerbated by the practice of many Ashkenazim to swallow the entire k'zayit at once. Why the vast difference? It began with a debate between RAMBAM and RASHI. RAMBAM writes that an olive is "less than" the size of a third of an egg. RASHI opines that it is the size of half of an egg. The opinion of RASHI was widely accepted, and is enshrined in the Shulchan Aruch. However, many present day rabbis have questioned this. RAMBAM lived first in Spain, then Morocco, then Egypt; all olive growing lands. RASHI lived in France. Olives don't grow in France. In all likelihood, he never saw an olive.Now the the question comes up, were the eggs the same size as ours? Most say yes. However, there is an apparent discrepancy between two statements in the Talmud on this point. The probable solution to this discrepancy is that one passage was talking about a square, and the other a circle. Nevertheless, one late 18th century rabbi declared our eggs to be half the size of the ancient ones. This opinion was enthusiastically adopted by a prominent 20th century rabbi. This view doubles the egg, as well as the olive. As opposed to this, many point out that olive trees in Israel and surrounding areas, some of which are still alive from before the destruction of the Temple, produce the same size as those which we have today. This is true as well of the olives uncovered in archaeological digs. As to the egg, some were found in the ruins of Pompeii They were a third SMALLER than our modern eggs. This opens up an entire topic, beyond the scope of this post. To what degree is empirical evidence a factor in halachah. Now, you may ask "what's the big deal? So eat more matzah!" The answer is that we are meant to rejoice in our Festivals. Stuffing vast amounts of dry matzah down our throats is unpleasant, dangerous, as well as superfluous. As an aside, I would add that the Sepharadi soft matzah (roughly the texture of pizza crust) is not difficult to eat. With some knowledge, Passover is the great joy it was meant to be, the Seder a celebration of past, present and future, without distraction of centuries of speculation and insecurity. It's easy when you know how!