In-situ calibration of the single-photoelectron charge response of the IceCube photomultiplier tubes. (1st June 2020) - Aartsen, M.G.; Ackermann, M.; Adams, J.; Aguilar, J.A.; Ahlers, M.; Ahrens, M.; Alispach, C.; Andeen, K.; Anderson, T.; Ansseau, I.; Anton, G.; Argüelles, C.; et al.