There is no erech [which is] less than a sela, nor more than fifty selaim. How so? [If] he gave a sela and then became wealthy, he gives nothing; [if he gave] less than a sela, and then became wealthy, he must give fifty selaim. [If] he had in his hands five selaim, R’ Meir says: He need only give one. But the Sages say: He must give them all. There is no erech less than a sela, nor more than fifty selaim. There is no [returning to the] beginning [of the niddah cycle] for one who erred [in her calculation] in less than seven [days] nor [in] more than seventeen [days]. There is no [confinement of] negaim for less than one week, nor for more than three weeks.