You are assigned a seniority number at the time you register for the specific job fair. Once at the job fair itself, groups of 50ish line up to speak with the recruiters. 1-50, 1-100, 1-150 etc. Gives you an idea of when you'll actually get to speak with someone and allows you to go sit down, relax, and stand around for hours at a time. Makes for a more civilized experience.