Study Avodah Zarah folio 9B with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
“48 cities” (Numbers 35:7). Similarly, if a scribe forgot the exact year, let him ask the tanna how many years does he teach have already been lost from the 2,000 years that are designated for the days of the Messiah. And he should deduct 48 years from the number, correcting for the century, and in this manner he will find his number. And your mnemonic to remember that the tanna must add to the date of the scribe, while the scribe must deduct from the number of the tanna, is again: A scribe deducts, while a tanna adds on [tosfa’a].
אמר רב הונא בריה דרב יהושע: האי מאן דלא ידע כמה שני בשבוע הוא עומד — ניטפי חד שתא, ונחשוב כללי ביובלי, ופרטי בשבועי.
§ Rav Huna, son of Rav Yehoshua, says: In the case of one who does not know which year of the 7-year Sabbatical cycle he stands in, he should add one year to the years that have passed since the destruction of the Temple in order to begin at the start of a Sabbatical cycle. And he should calculate the general years, i.e., the centuries, as Jubilee cycles, as every Jubilee concludes 7 completed Sabbatical cycles of 49 years, and the details as Sabbatical cycles, i.e., he should divide the remaining years into 7-year Sabbatical cycles.
ונשקל ממאה תרי, ונשדי אפרטי, ונחשובינהו לפרטי בשבועי, וידע כמה שני בשבוע, וסימניך: ״כי זה שנתים הרעב בקרב הארץ״.
But as the Jubilee Year itself is counted as one year of a Sabbatical cycle, he should take, from every 100 years that passed, two years, and add it to the details, i.e., the remaining decades and single years. And then he should calculate with the details by dividing them into Sabbatical cycles. And from the remainder he will know how many years in the current Sabbatical cycle have passed. And your mnemonic that two years must be deducted from every century is the following verse: “For these two years the famine has been in the land” (Genesis 45:6).