Trendlines come in three flavors: external, Internal, and curved. External trendlines do not cut through prices, but rest along the tops or bottoms of the peaks or valleys. Internal trendlines do cut through prices, so that is what differentiates an internal trendline from an external one. Sometimes price action is not straight, but curved. Draw a curved trendline along the peaks or valleys to identify this curved trendline. I read this very recently from a book called, Getting Started in Chart Patterns by Thomas N. Bulkowski. I hope Tradeview community found this valuable to learn.