Context: The theoretical difficulties arise from the fact that all of the methods except the X-ray crystal density method rely on the theoretical basis of the Josephson effect and the quantum Hall effect. If these theories are slightly inaccurate – though there is no evidence at present to suggest they are – the methods would not give accurate values for the Planck constant. More importantly, the values of the Planck constant obtained in this way cannot be used as tests of the theories without falling into a circular argument. Fortunately, there are other statistical ways of testing the theories, and the theories have yet to be refuted.

Question: Other than the X-ray crystal density method, other methods rely on what two effects?
Answer: the Josephson effect and the quantum Hall effect

Question: Why does relying on these effects create concern?
Answer: If these theories are slightly inaccurate

Question: Using Planck constant values from these effects would lead to what logical issue?
Answer: a circular argument

Question: What is the saving grace of relying on these theories?
Answer: there are other statistical ways of testing the theories, and the theories have yet to be refuted.

Question: Why is there no saving grace of relying on these theories?
Answer: Unanswerable

Question: What logical issue would using Planck constant values from these effects never lead to?
Answer: Unanswerable

Question: What theories have always been refuted?
Answer: Unanswerable

Question: What effects are never relied on?
Answer: Unanswerable