70 years of what?

The method of arriving at 607 BCE seems simple enough. How could anyone ignore the clear words of the Bible and put secular chronology above the inspired word of God? Any respectable apostate doesn't want to look like he's contradicting the Bible – that would put others off his attempts to discredit the 1914 doctrine and draw them out of the truth.

So instead, they twist the 70-year prophecy of “devastation” (or, ruins) to “actually mean” something else. If they manage to show that 607 is wrong, yet the 70-year prophecy was still fulfilled shown, then there is no reason why Jehovah's Witnesses should not accept the secular chronology. Accepting that, in turn, means the 1914 doctrine would have to be scrapped.

Typically, they use two different approaches. They claim it either “actually” means mere servitude to the King of Babylon for seventy years, or instead claim it “actually” means some sort of vague or figurative type of devastation for seventy years. They go to great lengths to argue that how long the city of Jerusalem lay in ruins is irrelevant. This is despite the scriptures ever-so clearly stating that Jerusalem would be in ruins without an inhabitant.

So, do the scriptures say the city of Jerusalem will lie in in ruins for a full seventy years, or not?