Well, let's qualify that claim just a bit: the errors in the result are actually pretty symmetric when the fractional error in the measurement is very small; it's only when the fractional error in the...Well, let's qualify that claim just a bit: the errors in the result are actually pretty symmetric when the fractional error in the measurement is very small; it's only when the fractional error in the measurement becomes large that the asymmetric mistake in result becomes obvious. In other words, when the uncertainty in a measured parallax becomes a significant fraction of the measurement itself, the chances are that the ACTUAL distance to the star is larger than the calculated distance.
