ok st in bg, How in the world did zecharia sitchen decipher the ancient tablets?

I mean like how could he decipher that their was a 10th planet with an eliptical orbit? What their pictures drawn on the tablets with a eliptical circle around both the suns that were drawn, like was their all the planets drawn in sizes on these tablets with this extra planet picture on these tablets with a oval shape showing nibiru's path? How did he know for sure the symbols on these tablets are correct in his interpretation of them?

How did he know how to decipher english words from the sumerian words , basically he is guessing, so how could he possible be that accurate when their are just a bunch of symbols that anyone could just guess their true meaning? Thanks for reading, Josh.