There were seveal crazy calculations by Russell who attempted to combine various era, years, jubelee and contemporary events to prove his points. In the Studies in the scriptures, he wrote numerous examples on how he got into this year. There are several pivotal years like 1799 in which Napoleon took over Rome, 539 with Justinan capture of Rome...
"While the time prophecies thus point to and harmonize with 1874 as the date of our Lord's second presence, assuring us of the fact with mathematical precision, we find ourselves overwhelmed with evidence of another character; for certain peculiar signs, foretold by the Lord and the apostles and prophets, which were to precede his coming, are now clearly recognized as actually fulfilled. We see that the promised Elias has indeed come; that his teachings have been rejected, just as predicted; and that therefore the great time of trouble must follow. The predicted Man of Sin, the Antichrist, has also made his appearance, and accomplished his long and terrible reign; and at the exact "time appointed" (1799) his dominion was taken away. The cleansing of the sanctuary was also accomplished as predicted, and at a time sufficiently in advance of 1874 to make ready "a people prepared for the Lord"--a people in devout expectancy of his coming--just as a similar work prior to the first advent made ready a people to receive him then. We find that the date 1874 is also in harmony with the prophecy of Daniel (12:1), which fixes the advent of "Michael" in the "Time of the End"--that is, somewhere between 1799 and 1914--and as the cause and precursor of the great time of trouble. When seventy-five years of this "Day of Preparation" had developed the proper conditions for the beginning of his great work, then the Master stepped upon the scene--quietly, "without outward show"--"in like manner" as he went away.