Russell used 536-70 to get 606, but WTS lie when they say Russell made a zero year error. He understood the maths far better than the WTS understood his work. The calculation can be found in Studies in the Scriptures vol 2 The Time is at Hand studyIV pgs 73 to 102. Russell calculates from the start of 606 to the end of 1914, 2300 years, how ever he makes it clear that he understands the zero year error Miller made with 1843, and in his chronology he understood that the Jewish years had their start in Trishri of the previous year. Therefore when he shows start 1915 or end 1914 it means Trishri or as he states it as October 1914.
Rev John Aquila Brown first produced a 7 times prophecy date using 604 the first year of Nebuchadrezzar as his start point, not the desolation of Jerusalem, and had an end date of 1917.
The 1799 is Russells date for the end of the papacy, 1260 yrs from it's inception in 539, from this start date using the 1335 yrs Dan 12 he reached 1874 and with the addition of 40yrs made up from the last week of the 70 weeks, 7years plus the 33 yrs between the end of the 70 weeks and the 2nd Roman destruction. The 1874 date was adapted from Millers original prophecy of 1843 by exchanging Millers 1290yrs which was deducted from the fall of the papacy with Russell's 1260 figure and thus advancing the invisible return by thirty years to 1874.
Hope this helps.