"Freeme" has the process quite correct with : Daniel 4:10-16: seven times / Revelation 12:6, 14: 3 1/2 times = 1260 Days => 7 times equals 2520 Days / Ezekiel 4:6: a day for a year = 2520 years / 607 b.c. Jerusalem destroyed / no zero year / 607 b.c + 2520 years = 1914.
Each of these steps has its flaws, the greatest being the WTS's incorrect date for the destruction of Jerusalem.
Russell, the founder and first President of the WTS, taught that Jesus Christ's "parousia" took place in 1874. He built a series of dated events that were based on that presumption. Russell foresaw a harvest period of 40 years ending in 1914, at which time the Zionists would bring in an unprecedented era of peace.
Russell's expectations failed. When Rutherford forcibly took over the reigns, he changed Russell's teachings. But even as late as 1930, Rutherford still taught that the "parousia" had taken place in 1874. So the current positions are based on Rutherford's reconstructions made during the 1930s.
Doug
Melbourne