[If] one says: ‘I take upon myself [to give] my weight,’ he gives his weight. If [he specified] silver, [he is required to give] silver; if [he specified] gold, [he is required to give] gold. [There was] an incident concerning the mother of Yirmatia, who said, ‘I take upon myself [to give] my daughter’s weight,’ and she went up to Jerusalem and they weighed her, and she gave her weight [in] gold. [If one says,] ‘I take upon myself [to give] the weight of my arm’ — R’ Yehudah says: He fills a cask [with] water and inserts [his arm] up to his elbow, and he takes donkey meat, sinews, and bones, and he adds to it until it fills up. R’ Yose said: Now how is it possible to determine precisely flesh against flesh and bones against bones? Rather, we estimate how much the arm is likely to weigh.