Many of the standard tag types have data values that can be plotted on the screen as live data. These tags belong to the Trenders tag group.

Logger tags are used to log the historical data values of any one of the tag types belonging to the Numeric tag group (encompassing tags belonging to the Trenders tag group). In other words, tags of the numeric tag group can contribute their data values to a logger tag. Tags whose data is being recorded by a logger tag (or "contributed" to a logger tag) can have their historical data values plotted on the Historical Data Viewer (HDV) page by VTS (see Historical Data Viewer Page).

When an analog input or digital input tag’s data has been plotted in the HDV, or if a logger tag has been configured to record data for a numeric tag, then a data file (.DAT) and a log file (.LOG) are generated by VTS for that tag.

For VTS applications, the .DAT and .LOG files are saved in the application's folder by default. In the case of VTScada applications, the .DAT and .LOG files are saved in the History subdirectory within your application directory, grouped by month and year.

The data file is the name of the tag whose data is being recorded with the extension .DAT, while the log file is the name of the tag whose data is being recorded with the extension .LOG. These files are in an encrypted binary format that cannot be edited manually.