Avodah Zarah, Daf Tet, Part 4
Introduction
Again, R. Papa uses the previous calculation of years to aid a scribe in remembering the year.
אמר רב פפא אי טעי תנא ולא ידע פרטיה כמה הוי לישייליה לספרא כמה כתיב וניטפי עלייהו ארבעין ותמני ומשכח ליה לחומריה וסימניך (במדבר לה, ז) ארבעים ושמונה עיר.
R. Papa said: If the Tanna does not know the exact number of years [of the period of the Messiah] that have passed let him ask a scribe what year he uses in his writings, and on adding forty-eight to it he will find his solution. And your mnemonic is, Forty-eight cities (Numbers 35:7).
If the tanna remembers how many hundreds of years have passed into the years of the Messiah, meaning the third period of 2000 years, but does not remember the exact number of years, he can ask a scribe who counts by the secular years and add 48. So for instance if it is the year 325 in the secular years then it must be the 73rd year of the Messianic cycle, plus whatever hundred they happen to be in.
ואי טעי ספרא נשייליה לתנא כמה קתני וניבצר מינייהו ארבעים ושמונה ומשכח ליה לחומריה וסימניך ספרא בצירא תנא תוספאה
If, on the other hand, the scribe is uncertain as to his number, let him ask the Tanna how many he counts and deduct therefrom forty-eight and he will find his solution. As a mnemonic, take the phrase, The Scribe is sparing, the Tanna is redundant.
As with above, this is simply the opposite situation.