Twitter community adds a context note to Concerned Citizen tweet: Twitter account "Concerned Citizen" tweeted, "Hey all you very stupid moon landing believers...... Explain this please?" The tweet included a photo showing a SCUBA diver with two tanks labeled "Oxygen for one hour," and a photo of an astronaut on the moon with a pack on his back, labeled "Apollo 17" and "Oxygen for 22 hours." Twitter added a label to the post that read "Readers added context they thought people might want to know." The added context read "[A]s the photo clearly show[s], the sub [sic] is carrying cylinders clearly marked 'compressed AIR', only 22%oxygen, no rebreathing system. Expired nitrogen, CO2 and unused oxygen bubbles away. Spacesuits carried pure Oxygen in a rebreathing closed circuit for 7 hours, not 22. en.wikipedia.org/wiki/Apollo/Sk…" Twitter users are able to sign up as contributors to add context to tweets.