There are both practical and theoretical difficulties in determining h. The practical difficulties can be illustrated by the fact that the two most accurate methods, the watt balance and the X-ray crystal density method, do not appear to agree with one another. The most likely reason is that the measurement uncertainty for one (or both) of the methods has been estimated too low – it is (or they are) not as precise as is currently believed – but for the time being there is no indication which method is at fault. COUNT 3
QSN1 What is a main practical difficulty in determining n? ANS1 the two most accurate methods, the watt balance and the X-ray crystal density method, do not appear to agree with one another QSN2 Why does this difficulty occur? ANS2 it is (or they are) not as precise as is currently believed QSN3 Which method is at fault or the discrepancy? ANS3 there is no indication which method is at fault