When talking about melting the lock to gain entry to the chemical warehouse, Walt says that the Nazi rail gun the "Schwerer Gustav," could not be destroyed by bombs, and in the end was destroyed by one man who parachuted in and melted the gun. In reality the Gustav was probably destroyed to prevent its capture. After the siege of Leningrad it was moved back to Germany and not seen again until Allied soldiers discovered it, destroyed, in eastern Germany.
When discussing alcohol with Hank, Walter says that if they had been drinking the liquor in 1930, it would have been illegal, and one year later it would have been legal. Prohibition in the United States did not end until the ratification of the 21st Amendment in December, 1933.
In the scene where Walter is drinking orange juice after having cooked, the right ear stem of Walt's eyeglasses is about an inch above his ear. When the camera cuts away to another view, his right ear stem has moved down an inch to be directly above his ear.
When Walt was talking about drinking, he says that in the 30's they would have been breaking the law. There where no rules against drinking during prohibition, only the sale and distribution of alcohol.
In the previous episode, Walt shaved his head when he discovered he had started losing his hair due to the chemotherapy, with bald spots at the sides visible. During the school meeting and afterward, you can actually see his head is just shaven but without any bald spots.