function which_chart() {
   now = new Date();
   hour = now.getHours();
   if (hour < 00 || hour >= 18) {chart="short_term_morgen1";}
   else
      if (hour >= 00 && hour < 06) {chart="short_term_vandaag1";}
      else {chart="short_term_vandaag2";}
   return(chart);
}
kaart=which_chart();
document.write('<iframe scrolling="no" src=http://www.knmi.nl/'+kaart+'.html height=285 width=220 marginwidth=0 marginheight=0 scrolling=no frameborder=0>');
document.write('</iframe>');