Updating a point in chart.

I am currently adding line to a chart to show when a value is ON and using the gap in a series feature to indicate when the value is OFF. In order for this to work I need to update the chart every few seconds when the value is ON; however, I do not want to add additional points; instead I want to either update a point in the line series or I want to remove a point and then add a new point. In my case its the x-axis value that I need to change.

Can you please suggest if this is possible?
If yes I am also wondering how to best find a specific point in a line series.