How to auto scale Y-values for a DateTime series within a zoomed in X boundaries?

Question

I am writing an application for Windows 10 using Delphi 11 and Steema TeeChart pro 11 components.

I use AddXY(….) to plot a DateTime series of about 1000 values as points in Chart1 with BottomAxis set to DateTime and the Leftaxis set to float.

Thereafter I zoom in a small part of the data in Chart1 using the mouse wheel or drawing a rectangle. Then I want to plot a new time series (AddXY(….)) of 1000 values in Chart1, keeping the zoomed in min and max values for the bottom axes, but use automatic scaling for LeftAxis. Before plotting the second series I delete the first.

The second series have the same DateTime values as the first series, but the Y values are sometimes very different compared with the first series and may not be visible in the graph.

Now the problem occurs. The Left axis will be automatic scaled based on all the data points and not on the points only falling within the zoomed X boundaries.

Does TChart have a simple method to find the min and max Y-values for the second series within the zoomed in time period. I thought of using the LeftAxis.AdjustMinMax() procedure for rescaling the left axis?

Of course I could scan through all the Y-values within the zoomed in period and calculate the min and max value. Then, how do I know the starting and ending valueindex of the data points falling within the zoomed in time period? I hoped to avoid using this method due to speed resons if number of points are > 1000.

Hopefully someone more experienced TeeChart programmer than I am can give me some suggestions of the best way to achieve this.