  The uncertainty relation formulated by Heisenberg in 1927 describes a
trade-off between the error of a measurement of one observable and the
disturbance caused on another complementary observable so that their product
should be no less than a limit set by Planck's constant. In 1980, Braginsky,
Vorontsov, and Thorne claimed that this relation leads to a sensitivity limit
for gravitational wave detectors. However, in 1988 a model of position
measurement was constructed that breaks both this limit and Heisenberg's
relation. Here, we discuss the problems as to how we reformulate Heisenberg's
relation to be universally valid and how we experimentally quantify the error
and the disturbance to refute the old relation and to confirm the new relation.
