You can obtain the hidden achievement "A Perfect Yesterday" by completing the "Fontaine Research Institute" questline - more precisely, during the stage "Fontaine Research Institute, Stagnating in the Rubble." This is crucial because it is at this point that the necessary door will open, leading directly to the achievement. Read on to learn how to earn "A Perfect Yesterday" and a couple of Primogems for it.

How to Unlock the "A Perfect Yesterday" Achievement

Head to the Fontaine Research Institute of Kinetic Energy Engineering, located in one of the buildings.

Inside the building, as seen in the photos above, there is something like an office. That's where you need to go: on the table across from the entrance wall, you will find a notebook that you should read.

Once you do this, the "A Perfect Yesterday" achievement will immediately unlock, and in the Archive, you will see a bonus of five Primogems marked with a red exclamation point.