The development and updating of the Stockholm Historical Weather Observations data set is a collaboration between the Swedish Meteorological and Hydrological Institute and Stockholm University.
Each individual barometer observation, back to 1 January 1756, has been used to create a record of sea level pressure (SLP), i.e. observed air pressure reduced to 0 °C, normal gravity and sea level given in the unit hPa. Corrections have also been made to adjust for known or supposed barometer biases. Additionally, homogeneity adjustments have been applied to force the Stockholm SLP series to have a long term trend that is in agreement with other long SLP records from northern Europe. The details of how this was achieved are given in Moberg et al. (2002) and the work was done within the European Union FP4 project IMPROVE - Improved Understanding of Past Climatic Variability from Early Daily European Instrumental Sources. Updates of the series through 2012 is made by merging with the recent observations made by the SMHI. Thereafter, these long data files are not updated, but observational data are available from 2013 onwards both for the manual and the automatic station here.
The non-homogenized SLP series does not include the corrections for known or supposed biased barometers and is not homogenized against air pressure observation series from other stations.