WeatherUnderground's new beta weather site (http://preview.wunderground.com/cgi-bin/findweather/hdfForecast?query=94965&MR=1) shows the use of three charts showing various weather variables with ONE slider over all three charts showing the values on all three charts. This multi-layered configuration of charts linked by one slider would definitely be great indeed as it avoids crowding too may items on one chart.