  The recent paper gr-qc/9909017 criticizes the limit on the measurability of
distances that was derived by Salecker and Wigner in the 1950s. If justified,
this criticism would have important implications for all the recent studies
that have used in various ways the celebrated Salecker-Wigner result, but I
show here that the analysis reported in gr-qc/9909017 is incorrect. Whereas
Salecker and Wigner sought an operative definition of distances suitable for
the Planck regime, the analysis in gr-qc/9909017 relies on several assumptions
that appear to be natural in the context of most present-day experiments but
are not even meaningful in the Planck regime. Moreover, contrary to the claim
made in gr-qc/9909017, a relevant quantum uncertainty which is used in the
Salecker-Wigner derivation cannot be truly eliminated; unsurprisingly, it can
only be traded for another comparable contribution to the total uncertainty in
the measurement. I also comment on the role played by the Salecker-Wigner limit
in my recent proposal of interferometry-based tests of quantum properties of
space-time, which was incorrectly described in gr-qc/9909017. In particular, I
emphasize that, as discussed in detail in gr-qc/9903080, only some of the
quantum-gravity ideas that can be probed with modern interferometers are
motivated by the Salecker-Wigner limit. The bulk of the insight we can expect
from such interferometric studies concerns the properties of "foamy" models of
space-time, which are intrinsically interesting independently of the
Salecker-Wigner limit.
