Is there a way to change the interval of data seen on a graph in a series.

I'm using Polar graphs and Line graphs to visualize some data.   
We have a lot of data points .  I would like to use a slider from 1 - 10 to chart the data at that rate
Currently I plot the data with a for loop like this:

for(int i = 1; i < data.Length()-1; i += sliderSteps)
{
    series.Values.Add(newValue[i]);
}

When I move the Slider
The slideSteps variable would change
I want to the charts data to update to show the data in that amount

I think I probably clear the series data,
Add it at the new intervals 
refresh the chart 
But this isn't giving me good results 

As a separte issue the charts don't visually update unless you click on them.  It's not very "live"