Conclusion: Choosing With Your Eyes Open
This companion opened by observing that RTK, the method the rest of this series assumed by default, is only one member of a larger family. Four methods later, that family is no longer a list of unfamiliar acronyms. It is a small, coherent set of answers to two simple, recurring questions.
Every correction method answers the same two questions, when and where, in its own deliberate way. Choosing well means knowing what a project actually needs from each answer, not defaulting to whichever method is most familiar.
The Family, One Last Time
RTK answers both questions in favor of immediacy: live, and dependent on a nearby reference. PPK keeps that nearby reference but trades immediacy for the better information a short wait provides. PPP gives up the nearby reference entirely, trading a convergence period for genuine independence from local infrastructure. PPP-RTK tries to recover much of RTK's speed while keeping much of PPP's freedom from dense local infrastructure, using a newer correction format built specifically to make that combination work.
No method in this family is obsolete, and no method is universally correct. Each one remains the right tool for the specific combination of circumstances it was built to answer well.
What This Companion Has Actually Been Teaching
Underneath the acronyms, this companion has been teaching the same habit the rest of this series has built from the very first chapter of Companion One: understand what produced a number before deciding what that number means. A correction method is simply the earliest, most fundamental choice in that chain, made before a reference frame is ever assigned, before an epoch is ever recorded, before any question of trust or verification even applies.
Choosing a correction method deliberately does not mean avoiding a dependable default. It means understanding why that default fits most of the time, and recognizing the moments, like establishing control others will rely on, that call for something else. That is the same discipline this entire series has been built around: knowing exactly what produced a coordinate, so that everything built on top of it, its frame, its epoch, its accuracy, and its trustworthiness, rests on an informed decision rather than an assumption.
Whichever method produces the next coordinate this companion's method is applied to, the choice, whether it is the same dependable default used every day or a deliberate departure from it, will have been made with a clear understanding of what was actually being traded away, and what was actually being gained.