The MaxYValue property returns the largest Y value in the chart series, it does not return you the index of the data point (which would be needed in order to get the corresponding X value). You could walk the series YValues[index] until you found the yvalue that = MaxYValue, which would then give you the index, but if there are 2 data points where the YValue = MaxYValue, then you would not be able to determine what data point you needed to get. Eg, given the 6 sample data points in the format of index = (x, y)

0 = (1, 5)

1 = (2, 7)

2 = (10, 20)

3 = (11, 14)

4 = (15, 12)

5 = (8, 20)

The series MaxYValue would return 20. But because there are 2 data points with Y=20, you would be unable to determine if the corresponding X value was supposed to be 10 or 8. So, only if EVERY y value and EVERY x value is unique, will you be able to do what you are asking.

Russell