RichTextBox ScrollBar Position

Question

Hi, I' have a richTextBox that display incoming data. 

The problem is that, the scrollbar by default stays on the topmost position whereas I want it to scroll down to the latest data coming in which is appended to the bottom of the richTextbox. 

And if/when a user scrolls up to the middle position of the box, the scrollbar should NOT scroll to the latest data coming in. Instead, it should just stay on the position the user has scrolled up to. 

How do I go about this? 

Thanks. Im using C# btw.