Anniversaries and milestones are a good time for reflection. (For example, this is the 100th Great Job, Internet post… feel free to reflect back on how awesome that weird Norwegian “Let It Be” video was.) Billboard and Lady Gaga enjoyed a milestone together this week when “Born This Way” became the 1,000th No. 1 single since Billboard started keeping track. What better way to celebrate than going back in time and listening to every single since 1956 to share that top spot with Gaga, 5 seconds at a time? All it will require is an hour and a half of your time and a willingness to overlook any music that came after 1992, since that’s where this two-part song collage cuts off. If you feel need to relive the hits that came after that, mosey on over to our THEN That’s What They Called Music and This Was Pop columns to fill in the blanks.