First M87 Event Horizon Telescope Results. III. Data Processing and Calibration, The Event Horizon Telescope Collaboration, Akiyama, Kazunori, Alberdi, Antxon, Alef, Walter, Asada, Keiichi, Azulay, Rebecca, Baczko, Anne-Kathrin, Ball, David, Baloković, Mislav, Barrett, John, Bintley, Dan, Blackburn…