The daily and monthly mean total ozone observations in this dataset were digitized from "Ozone Data for the World", published by the Meteorological Service of Canada in cooperation with the World Meteorological Organization (WMO).

The published monthly mean total ozone values were sometimes found to be in error, in which case the errors were corrected in the digitized version. Some stations revise and correct previously published values of ozone which were in error perhaps because of lack of instrument calibration or an error in data reduction techniques.