File talk:Leapsecond.ut1-utc.svg

Suggested simpler script

The disadvantage of this script is that you have to set the xrange in a less-natural format; the advantage is that it uses only the MJD field and not the more tricky Y-M-D fields.

Wrapper script

   wget http://maia.usno.navy.mil/ser7/finals.all
   
   cut -c 8-15,58,59-68 --output-delimiter " " finals.all > finals-cut.txt
   grep "P" finals-cut.txt > finals-pred.txt
   grep "I" finals-cut.txt > finals-iers.txt
   
   gnuplot leapsecs.gnuplot

leapsecs.gnuplot

   set xdata time
   set timefmt "%s"
   set format x "%Y"
   set xrange ["442126800":"1357362000"]
   set grid lt 3 lc 0
   unset key
   set terminal svg
   set output 'Leapsecond.ut1-utc.svg'
   plot 'finals-iers.txt' using (($1-40587)*86400):3 w l lt 2 lc 2 title 'Measured', 'finals-pred.txt' using (($1-40587)*86400):3 w l lt 1 lc 1 title 'Predicted'

The interesting things here are that timefmt "%s" specifies Unix-time (seconds since 1970-01-01 00:00:00 UTC); the xrange is specified in these units (and yes, the quotes are necessary), and the X formula becomes ($4-40587)*86400 — 1970-01-01 is JD 40587, and 86400 seconds per day.