In real experiments very often an upper bound for the uncertainty of one of the conjugate variables, say , is given - as a
property of the measuring device (slit). The corresponding is identified with the single-particle uncertainty - but this is a very
rough estimate which does not do justice to the universal validity of the IUP claimed by its inventors. In order to know the real
for particle one should be able to measure the position of particle within the slit - and no such experiment has ever been
performed