A diagonal surface in a link exterior M is a properly embedded,
incompressible, boundary incompressible surface which furthermore has the same
number of boundary components and same slope on each component of the boundary
of M. We derive a formula for the boundary slope of a diagonal surface in the
exterior of a 2-bridge link which is analogous to the formula for the boundary
slope of a 2-bridge knot found by Hatcher and Thurston. Using this formula we
show that the diameter of a 2-bridge link, that is, the difference between the
smallest and largest finite slopes of diagonal surfaces, is equal to the
crossing number.Comment: 16 pages, 6 figure
