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The Maunder minimum (MM) of greatly reduced solar activity took place in1645-1715, but the exact level of sunspot activity is uncertain as based, to alarge extent, on historical generic statements of the absence of spots on theSun. Here we aim, using a conservative approach, to assess the level and lengthof solar cycle during the Maunder minimum, on the basis of direct historicalrecords by astronomers of that time. A database of the active and inactive days(days with and without recorded sunspots on the solar disc respectively) isconstructed for three models of different levels of conservatism (loose ML,optimum MO and strict MS models) regarding generic no-spot records. We haveused the active day fraction to estimate the group sunspot number during theMM. A clear cyclic variability is found throughout the MM with peaks at around1655--1657, 1675, 1684 and 1705, and possibly 1666, with the active dayfraction not exceeding 0.2, 0.3 or 0.4 during the core MM, for the threemodels. Estimated sunspot numbers are found very low in accordance with a grandminimum of solar activity.  We have found, for the core MM (1650-1700), that: (1) A large fraction ofno-spot records, corresponding to the solar meridian observations, may beunreliable in the conventional database. (2) The active day fraction remainedlow (below 0.3-0.4) throughout the MM, indicating the low level of sunspotactivity. (3) The solar cycle appears clearly during the core MM. (4) Thelength of the solar cycle during the core MM appears $9\pm 1$ years, but thereis an uncertainty in that. (5) The magnitude of the sunspot cycle during MM isassessed to be below 5-10 in sunspot numbers;  A hypothesis of the high solar cycles during the MM is not confirmed.

Level and length of cyclic solar activity during the Maunder minimum as deduced from the active day statistics