Measurements are stored in archive files that exist in the working directory as *.d2i files and in the archive directory as *.d2 files. By default, these two directories point to the same location, which is the Archive folder in the openHistorian installation directory. For some more in-depth information on where data is stored, the following post in the section titled The openHistorian file format describes the various stages the data will go through as it’s written to the historian.