Casting Essentials: Straight Line Path

“OK, so how do I know if my rod tip is following a straight line or not?”
Ok then – you can tell exactly what your tip path is doing by looking at the loop as explained and shown in the clip.

Here it is again:
A large wide open loop results from a large open convex tip path
A tailing loop (or closed loop) is the result of a tip path that has traveled a slightly convex path.
A tight loop is a consequence of the rod tip traveling in a relatively straight path with a crisp efficient stop with the rod tip maintained high after that stop. i.e don’t drop the rod tip and tear open the loop after you send it on it’s way.

WIth regard to loop shapes:
 The top leg (the fly leg) of the loop is determined by the path of the rod tip prior to the stop.
The shape of the bottom leg (the rod leg) is determined by the tip path after the stop.
The shape of the loop face and the distance between these two legs is primarily dictated by what the rod tip does during the stopping sequence. The process that usually takes milliseconds.

Hope that helps.