gnuplot -persist << EOF
set ylabel "altitude (m)"
set y2label "error"
set xlabel "time (s)"
set xtics border out nomirror
set ytics border out nomirror
set y2tics border out nomirror
plot "$1" using 1:3 with lines axes x1y1 title "raw height",\
"$1" using 1:21 with lines axes x1y2 title "error"
EOF