Level and length of cyclic solar activity during the Maunder minimum as deduced from the active-day statisticsJ. M. Vaquero, G. A. Kovaltsov, I. G. Usoskin, V. M. S. Carrasco and M. C. GallegoA&A, 577 (2015) A71DOI: https://doi.org/10.1051/0004-6361/201525962