How should unwanted altitude information be deleted from a flight progress strip?

Marking unwanted altitude information for deletion with an 'X' is the appropriate method because it clearly indicates that the information is no longer relevant while still allowing others to see what has been removed. This helps maintain clarity and ensures that air traffic control personnel can quickly identify the changes made to the flight progress strip.

Using an 'X' serves as a visual cue that signifies the information has been reviewed and should not be considered for further reference. It indicates that the controller has actively decided to disregard that piece of information, enhancing communication and reducing the risk of misunderstandings.

Other methods, such as erasing the information completely or highlighting it in red, could create confusion or imply that the information was never there in the first place. Drawing a line through it without marking might also leave it open to interpretation, as it does not provide a clear signal about the status of that data. Marking with an 'X' is a standardized practice that promotes consistent handling of flight progress strips among controllers.