Looking back at the analog days, mixing level requirements seemed so easy. You aimed for 0 on the VU meter and didn’t worry too much if it bounced over. Of course, under the hood 0VU could actually be calibrated to different levels, but we usually didn’t concern ourselves too much with that as long as it was clean around the 0 mark. These days there are so many different meter reference calibrations available that it can take some time to settle on one that you feel comfortable with. That said, LUFS looms large when it comes to delivery signal levels, and that makes for lots of confusion.