All good advice but somewhat conflicted. I've tried doing this myself and I've been tripped up by their craftiness. I think JW Facts said it best, in my opinion. Keep us posted on how it goes.
Anyway, in a week,maybe less, he wants to discuss that date and why I don't support it. Keep in mind that my dad is an elder(one of the more reasonable ones) and is also a math wiz. So is there anything I can use that will show him that it can't be correct? I want to keep it simple as too much info will help no one. lol.
He's a math whiz so I would try AlleyMom's angle as suggested by AnnOMaly. Just work out the numbers using only the Watchtower material referenced.
His defense was the typical JW responce...that JW's rely only on the bible and not worldly historians, who don't have a love of the scriptures bla bla bla.
There are no dates given in the Bible, so how in the world can anyone determine what the date is if one relied only on the Bible? That question should open his mind as he needs to figure out how any of the dates are determined.
He also said that non-JW sources rely on the Gregorian calender while JW's rely on the lunar calendar or some other nonsense.
But the date, 539 B.C.E. is given in terms of the Gregorian calendar. Even down to the month that it was suppose to happen (October?). How could the witnesses rely on the lunar calendar without converting it over to the Gregorian calendar? Wouldn't it make sense that the non-witness sources did the same thing.