Back in the days of 35mm film, movies were delivered to theaters in individual reels. A typical movie would be five to seven reels long.

It was my Thursday job to tape all the reels together into one long piece of film for the Friday premier. I’d also have to build the trailer packs, add cues for lights down/up… just generally make sure that the movie would work as it’s supposed to.

For reference, you see that platter of film in the OP picture? That platter was delivered in chunks, and building the print is putting all those chunks together to make a complete movie.

I’d absolutely do an AMA if there were a mechanism to do so.