פירוש על עבודה זרה 17:9

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.