I spent yesterday afternoon at the Beinecke Rare Book and Manuscript library at Yale.
There's a really good post past the jump, so keep reading:
"In my collection of Geniza documents on the India trade there are many instances of paper sent as presents, but the quantities involved were always limited, between 12 and 36 sheets, although the donors and receivers were substantial businessmen. Thus, a consignment of 500 sheets must have been on a commercial basis, which is also implied by the text" (A Mediterranean Society, vol. 5, p. 457).After giving the students a moment to review the letter, I will tell them that I am going to send around an important artifact of modern life, at which point I will pull out a ream of paper. I will ask them to examine it and share what they notice in light of having read the letter from Halevi. What I'm hoping they'll see is that a ream of paper in modernity is still 500 sheets, that is, that a commercial unit of paper has been the same size that it is now for almost a thousand years.