eruvin 14

calculating in the perfect v. seeing what happens in the real world

(the formula circumference = 3 x diameter of a circle is used to calculate the equivalent of a round beam to a square beam. and is derived from the measurements of a large round water tank in the Temple. later in the page when the sideposts dimensions are debated, Abaye teaches to just go out and look at what people are actually doing. the theoretical occasionally gives way to the actual)