Frage zu gnuplot / set label

    // Die Daten mittels gnuplot visualisieren

    $gplotx   = 'set format x "%d-%m\n%H:%M"';

     $gplothdr = "

                set terminal png size 600,300 

                set output '" .$tempverlauf_pic. "'

                set timefmt '%Y-%m-%d_%H:%M:%S'

                set xdata time

                set title ''  

                set ylabel 'Temp °Celsius'

                set y2label 'Luftfeuchtigkeit (%)'

                set ytics nomirror

                set y2tics

                set grid

                set xzeroaxis lt -1 lw 1

                set yrange [" . $temp_min. ":" .$temp_max. "]

                set label  at '".$temperatur_min_datum."_".$temperatur_min_zeit."',".$temperatur_minimum." point lt 3 pt 7 ps 1.4 

                set label  at '".$temperatur_max_datum."_".$temperatur_max_zeit."',".$temperatur_maximum." point lt 3 pt 7 ps 1.4 

                plot '".$verlauf_source."' using 1:2 smooth csplines lw 2 axes x1y1 title 'Temperatur (°C)' with lines,\

                     '".$verlauf_source."' using 1:3 smooth csplines axes x1y2 title 'Luftfeuchtigkeit (%)' with lines