Hi,

You can try using the following code:

private void Timeline1_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)

        {

            Point pt = e.GetPosition(this.Timeline1);

            double value = this.Timeline1.Axis.GetPixelValue(pt.X);

            NumericTimeEntry entry = new NumericTimeEntry() { Time = value, Title = "New Entry" };

            NumericTimeSeries series = this.Timeline1.Series[0] as NumericTimeSeries;

            series.Entries.Add(entry);

        }

In the case you are working with DateTime values you can convert the value to DateTime with:

DateTime time = new DateTime((long)value);