Median PWV per month over 1997–2017 in the Chajnantor Plateau. The dots indicate the median value of PWV in this year, while the straight line indicates the trend for the PWV over the period of the study, with a possibility of projecting future PWV values. The median for all the monthly slopes is −0.001 ± 0.014, that is, consistent with zero. We do not see a long-term increase or decrease in the atmospheric variable of interest for Chajnantor.