  Although Heisenberg's uncertainty principle is represented by a rigorously
proven relation about intrinsic indeterminacy in quantum states, Heisenberg's
error-disturbance relation (EDR) has been commonly believed as another aspect
of the principle. However, recent developments of quantum measurement theory
made Heisenberg's EDR testable to observe its violations. Here, we study the
EDR for Stern-Gerlach measurements. In a previous report [arXiv:1910.07929], it
has been pointed out that their EDR is close to the theoretical optimal. The
present note reports that even the original Stern-Gerlach experiment in 1922,
the available experimental data show, violates Heisenberg's EDR. The results
suggest that Heisenberg's EDR is more ubiquitously violated than it has long
been supposed.
