TAI is one realization of TT that must be determined instantly from a
world-wide network of atomic clocks.  As expected, after-the-fact
analysis of the world-wide atomic clock data allows determination of better
realizations of TT, and the ttbipm.dat file contains one such corrected
realization.  This file is obtained by, e.g.,

wget ftp://ftp2.bipm.fr/pub/tai/scale/ttbipm.08
mv ttbipm.08 ttbipm.dat

The files ttbipm.nn tend to be published early in the year nn+1, (i.e., the
year 2009 for the ttbipm.08 file) so yearly downloads are required to keep
ttbipm.dat up to date.  For each ttbipm.nn file, there exists some header
lines (30 of them for ttbipm.08) that must be skipped before actual data
appear in the file. Thus, the NSKIP_LINES variable that appears in
CMakeLists.dat must be confirmed/reviewed each year after the download of
ttbipm.nn.

