Visibility data are fundamental meteorological data widely used in many
fields such as climate change, atmospheric radiation, atmospheric
pollution, and environmental health. Calculating the average visibility
is typically the first step when using visibility data. However, this
study proves that the algorithm previously used to calculate average
visibility is incorrect, leading to a non-negligible error in average
visibility data. Moreover, the use of this incorrect algorithm not only
artificially reduces the reliability of visibility data, but also
affects the credibility and even the correctness of the conclusions
reached in previous studies using visibility data. Therefore, we present
the correct algorithm for average visibility, which should be applied to
both future and previous research to significantly increase the
reliability and application scope of visibility data.