Sizing up Shiurim: Modern-Day Measuring—Up or Down?

 https://www.halacha2go.com/php/h2go/home2.php?number=724

Another contemporary posek, Rav Chaim Na’eh (early 20th century), extensively researched the matter, and among other calculations, based his measurements on the weight of a certain dirham (mid-Eastern coin)—a tradition going back in time to the Rambam (12th century early halachic authority). He reached an opposite conclusion: we should downsize our shiurim based on the current physical reality. Rav Chaim Na’eh’s revi’is measures 86.4 ml. At that time in Yerushalayim (where Rav Chaim was rav), this shiur was universally accepted. Today it is the common shiur in most of the world, and the Chazon Ish shiur is categorized as an extra chumrah (stringency).