What is the underlying argument between the Chazon Ish and Rabbi Chaim Naaeh and Reb Moshe Feinstein? I know they argue in amounts, but what is the underlying argument? How did each get the Measurement he got, why do they argue, and what about?
From what I've heard, it all starts with how you measure a "thumb-width", and from there multiply up to "handbreadth" (tefach), "cubit" (ama), and so on. The thumb-width question is whether it's measured from the narrower or wider part of the thumb.
Another issue, though perhaps unrelated to the above opiners, is that these measurements are not stable with human appendages being a siman. Rather, the width of an average thumb defines the measurement, which can change with changing generations. Rav Moshe uses this logic (quoting the Chasam Sofer/Chavos Yair) as one apology for why the Chasam Sofer had a larger shiur than he.