How have the courts treated the Miranda warning?

Appellant maintains his confession was fundamentally unfair and inadmissible against him, since counsel had not been appointed for him at the time he confessed. The record on appeal nowhere indicates that appellant had requested counsel prior to his being taken into custody by the federal agents or thereafter, prior to his confession. The federal agent advised appellant of his rights in accordance with Miranda v. Arizona, 384 U.S. 436, 86 S.Ct. 1602, 16 L.Ed.2d 694 (1966). The appellant admitted that he had read the form entitled "Your rights" which included the Miranda warning and that he fully understood it. He signed the form in the presence of the agent. He further admitted the agents had read to him his constitutional rights, based on Miranda, and that he had personally read his constitutional rights and "he understood them pretty well."