how to use C# MSChart to write the trigger mode like oscilloscope?

Question

I have a MSChart to show the data in time. X Axis is timer controller, Y Axis is Data. I had already written the Y-Div & Y-Offset function. But now I would like to write the trigger mode like an oscilloscope. Trigger mode have

1. Auto mode,
2. Normal mode.

How can I write the code of trigger level line, that up down the line to decide if the data show on MSChart? Thanks!