How to select a ray path to trace sequentially

FRED's default raytrace mode is non-sequential, but the user also has the option to switch to a sequential raytrace. One common scenario is that a user might have performed a non-sequential raytrace and is viewing the Raytrace Paths Report, or Stray Light Report and having identified a path of interest will next want to trace it sequentially. 

First, right-click on the path of interest and select Copy to User-Defined Path List.

Next, open the Advanced Raytrace dialog (again), and switch the Raytrace Method to "Sequential using a user-defined path", choosing the path that has just been saved.

Note: the path details can be viewed/edited via Raytrace / User-defined Ray Paths...