I am using Vb.Net - Visual Studio 2015

I have a chart to which I am adding points at regular intervals as I sample a real world measurement (like an oscilloscope). The x axis is time and the Y axis is the value. The data that is graphed is selected by the user from any one of a hundred different data streams so I want the Y axis to automatically scale (which it is doing by default).

However, after a period of time, the data series has enough points that the chart starts to bog down and affect the responsiveness of the GUI. (The user may add up to 10 series per chart and there are four charts.) I want to limit the number of points in the series to a value that it can handle without responsiveness issues. So, once the number of points in the series reaches the maximum that I want to allow, I remove the oldest point from the collection each time I add a new one to the series using the following lines:


This works to remove the oldest point and my series stays fixed at the desired number of points.

The issue is, once I begin removing points from the series like this, the Y axis autoscaling quits working.

Any ideas why this happens? Or a way around it?

Thanks in advance.