--On Wednesday, July 10, 2013 14:50 -0400 Donald Eastlake <d3e3e3@xxxxxxxxx> wrote: > The IETF values cross area interaction at IETF meeting and > attendees have always been encouraged to attend for the week. > Allowing one day passes is a recent phenomenon to which some > people, including myself, are on balance opposed. I would add that the registration fee covers a number of IETF expenses that are fixed and independent of the number of people-days at a meeting. So, independent of Donald's concern, even if one were to use a formula similar to the one you suggest it would be more like (1/5 * day-cost-part-of-fee) + fixed-expense-part-of-free or at least a much larger fraction of the latter. john