Anachronisms: The family gathers to listen to the reports of the Armistice Agreement Terms on a radio. However, broadcasting in Germany didn't start until 1923 and was strictly experimental and limited before that. This scene took place in 1918.
Factual errors: During the World War One period and immediately after Hitler sported a traditional "handlebar"-type mustache. He adopted his trademark "comb" mustache shortly thereafter. In any event, all known photographs of Hitler as an adult show him with a mustache of some style.
Anachronisms: The carpet in Max's house is an IKEA model from 2003.
Anachronisms: The cigarette lighter used by Max is a type that didn't exist until after WWII.
Anachronisms: Most of the props, costumes and cars date from either the late 1920s or the 1930s.
Anachronisms: During an early scene in the steelworks/gallery a worker is shown cutting up a locomotive for scrap. He is using an arc welder which was not in use until the second world war.
Anachronisms: The song "Happy Birthday to You" is sung at the party, but it did not appear in the form we know today until 1924.
Factual errors: Amongst the drawings of Hitler's "future world" at the end of the film, there are at least two buildings (including the Volkshalle, which was never built) actually designed by Albert Speer, who did not meet Hitler until 1930.
Factual errors: When Max sees Hitler for the first time, he correctly calls him "Corporal", but the uniform Hitler is wearing has no rank insignia. German Army uniforms in both world wars displayed NCO ranks on the collar.