set grid
set datafile separator ","
set title "RV G.O Sars Survey July 2008\nPlot of latitude and ship speed as function of survey day #\n"
set xlabel "Survey day #"
set ylabel "Latitude [decimal degrees]"
set yrange [70:75]
set xrange [0:]
set y2label "Ship speed [kt]"
set y2range [0:15]
set y2tics border
set y2tics 0,3,15
plot 'navdata-stage-1.txt' using (($1-1214807740)/86400):4 with line lt 1 title "Latitude",\
 'navdata-stage-1.txt' using (($1-1214807740)/86400):9 with line lt 2 axes x1y2 title "Ship speed"