private static TimeSpan getDuration(TimetableField field)
{
string input = field.duration;
Double time_duration = 2;
Double.TryParse(input, NumberStyles.Number, CultureInfo.GetCultureInfo("cs-CZ"), out time_duration);
int hours = (int) time_duration;
int minutes = (int) (time_duration-hours)*60;
return new TimeSpan(hours, minutes, 0);
}