My Dad in retirement was restoring covered bridges in NH and Vermont. I was driving with him circa 1992 to the different bridges and he was using a handheld Garmin to map their positions. He cursed SA for its making the positions less accurate. A large percentage of new civilian receivers use all four worldwide GNSS systems (Japan and India have regional systems). If SA was turned on for GPS, they can rely on the other three systems. So yes, SA is useless today.
That’s good to know.
I always wondered how effective SA was. With it enabled, there was still decent accuracy. Maybe 50ft. Certainly accurate enough for a missile targeting system. So maybe the conclusion from the government was why bother. However I do believe that there is more to SA - a simple encryption algorithm could disable the system completely.
Also, where are the other satellites positioned? Satellite positioning is important. Also, the number if satellites affects accuracy.