Draw a vertical line on a chart

Hi there,
I have a chart on wich a timeline is on the X-axis. It holds 7 days in the screen.
The data are shifting trough the chart from right to left as time passes, so the view changes every minute like a running sinusoide.
I want to be able to recognize the days in the chart by drawing a vertical line every time a day has passed in order to get an insight on where the day has changed.
How can I draw this vertical line on a chart and make it travel along the X-axis as time passes?
Thanks,
Jos
I have a chart on wich a timeline is on the X-axis. It holds 7 days in the screen.
The data are shifting trough the chart from right to left as time passes, so the view changes every minute like a running sinusoide.
I want to be able to recognize the days in the chart by drawing a vertical line every time a day has passed in order to get an insight on where the day has changed.
How can I draw this vertical line on a chart and make it travel along the X-axis as time passes?
Thanks,
Jos