For all of the huge, franchise-spanning questions that fans were waiting for Star Wars: The Last Jedi to answer, the real central question that drove most of the action in the new movie was a new, highly technical one. It's also one that anyone who watched Rogue One incredibly closely last year may have already seen coming. That's right — eagle-eyed Star Wars fans have pointed out that there was a small Easter egg in Rogue One that explains The Last Jedi's central question about spaceship tracking. Jyn Erso to the rescue, yet again!
The First Order gets a scary upgrade on their space fleet in The Last Jedi, which allows them to continue chasing the Resistance ships even after they enter hyperdrive. This is a totally new concept to the Star Wars universe — famously, all that Luke Skywalker, Han Solo, or any other pilot had to do to get to safety back in the day was hit hyperdrive on their craft and they'd zoom off lightyears away. But in the new movie, the First Order ships are able to show up to the exact spot that the Resistance ships disappeared to through hyperspace just moments later. We find out later in the movie that General Hux had Snoke's ship equipped with some big, complicated tracking device that is able to follow spaceships even through hyperspace (Rose Tico and Finn spit out some quick science-y stuff to explain how it works, but damn if it made any sense to me). Anyway, the important thing is that Jyn Erso actually found the plans for this tracking device in Rogue One!
It is totally understandable if you missed the moment while watching Rogue One last year since it was so small, and also wouldn't stand out unless you had already seen The Last Jedi. There's one quick scene where Felicity Jones' Rebellion fighter Jyn Erso gets into an Empire computer system, and she finds schematics for a hyperspace tracking program, as pointed out on Reddit. It looks like the Empire and First Order have been planning for General Hux's advanced tracking device for decades.
Since Rogue One takes place directly before 1977's A New Hope, and The Last Jedi is set about 35 years after that event, we are given the understanding that this tech has been in development for a very long time before it's actually used for the first time in the new movie. This little nugget in Rogue One will also go a long way for Star Wars diehards, some of whom were already starting to ding the introduction of the hyperspace tracking system as a canon-breaking plot device.
And the fun doesn't stop there — The Last Jedi also includes another nod to Rogue One in its standoff scene on the salt planet at the end of the movie. The director of Rogue One, Gareth Edwards, gets a small cameo as a First Order soldier. You can see him during that standout scene where a soldier in the trenches tastes what looks like the snow covering the planet, and exclaims "Salt!" Edwards is the guy who looks over next to the salt guy.
Clearly, there are a lot of small details going on in these movies that can be very satisfying if you pick up on them, even though it will probably take a couple rewatches to notice the subtle ones. I guess now that The Last Jedi is out, it's time to go back and rewatch the earlier movies yet again to see if you can find any more tiny details like the hyperspace tracking one in Rogue One that help connect the universe even more.