Data availability and file formatThe file format is a column-based plain text file with one file for each day of observations from each instrument. The data usually consist of the date, time and location of the measurement along with the measurement itself and an estimate of the error on that value. In addition to these we add several other quantities describing the atmosphere at that location and time. The full list is given in the table below. Those quantities marked with an asterisk (*) are used as co-ordinates and may be used to specify limits in the search process.