set terminal png large size 1000,800
set out 'LINE1.png'
set xdata time
set timefmt "%s"
set format x "%d %b %Y\n%H:%M:%S"
set title "Gravity data, GOS-2008. Plot of ship speed for LINE1"
set grid
set xlabel "Time [UTC]"
set ylabel "Ship Speed [kt]"
plot "gravity-GOS2008-line-01.txt" using 1:10 title 'Ship speed' with lines