The source_ID and site_ID should correspond to unique combination of long/lat (and vice versa).
Sometimes it seems that it is not the case and this seems to happen both for isotope data as well as for calibration dataset, so let's create a specific helpful error message about it.
The source_ID and site_ID should correspond to unique combination of long/lat (and vice versa). Sometimes it seems that it is not the case and this seems to happen both for isotope data as well as for calibration dataset, so let's create a specific helpful error message about it.