Understanding the Gradient Tool

After months of laying track for my Coast Route I still don't grasp the circumstances that allow or disallow the ability to delete a gradient marker (yellow arrow) at various locations. In some cases they may be deleted, in others they simply wont go away, but I have not been able to discover why. I try not to have any more than necessary to make a smooth transition.
Any insight?
By the way, I'm new here to the forum and appreciate all the work you all have done thus far. I've been around off and on since the first release of MSTS but left it alone for years after becoming frustrated with it. RW has me interested again. After nearly a year of experimenting with it I decided to tackle my Coast Route Project again. Much better experience this time around.
Any insight?
By the way, I'm new here to the forum and appreciate all the work you all have done thus far. I've been around off and on since the first release of MSTS but left it alone for years after becoming frustrated with it. RW has me interested again. After nearly a year of experimenting with it I decided to tackle my Coast Route Project again. Much better experience this time around.