  Ozsvath and Szabo have defined a knot concordance invariant tau that bounds
the 4-ball genus of a knot. Here we discuss shortcuts to its computation. We
include examples of Alexander polynomial one knots for which the invariant is
nontrivial, including all iterated untwisted positive doubles of knots with
nonnegative Thurston-Bennequin number, such as the trefoil, and explicit
computations for several 10 crossing knots. We also note that a new proof of
the Slice-Bennequin Inequality quickly follows from these techniques.
