function monatwechsel(monat_start,monat_end,monat_nr)
{
var monatstart = document.getElementsByName(monat_start)[0].selectedIndex;
var monatend = document.getElementsByName(monat_end)[0].selectedIndex;

if (monatend < monatstart)
{
if (monatstart + monat_nr > document.getElementsByName(monat_end)[0].length - 1)
{
monat_nr = 0;
}
document.getElementsByName(monat_end)[0].selectedIndex = monatstart+monat_nr;
}
}

function tagewechsel(tag_start,monat_start,tag_end,monat_end)
{
var monatstart = document.getElementsByName(monat_start)[0].selectedIndex;
var monatend = document.getElementsByName(monat_end)[0].selectedIndex;
var tagstart = document.getElementsByName(tag_start)[0].selectedIndex;
var tagend = document.getElementsByName(tag_end)[0].selectedIndex;
if (tagend < tagstart && monatend == monatstart)
{
document.getElementsByName(tag_end)[0].selectedIndex = tagstart;
}
}