The exact circle around a 4x4 square is 16.8 amut circumfrence. we settle for a circumfrance of 18 by putting the 24 people on the outside and calculating the inner circle (2 amut smaller in diameter). QUESTION Why didn't R.Yochanan use 23 people which produces an inner circle of 17 amut?
Ben Zion Gold, Israel
It seems from the Rishonim that "Lo Dak" means not that Rebbi Yochanan was careless in his math, but rather that he wanted to give a generous measure so that the Sukah would definitely be Kosher.
When we give Shiurim, they must be exact. The Shi'ur for a normal Sukah is 4 X 4. Rav Yochanan is not being Mechadesh anything in the Shi'ur but rather is giving practical advice for how to measure a round Sukah and therefore he widened the measure.
(See also Daf-Insights to Sukah 8:1.)