If you change the configuration of your trend history files (in an existing project), or you change the configuration of a trend tag that affects the number, time, or period of the trend files, you need to delete the existing trend files - before you run the new system.
If you change the path of your trend history files (in an existing project), existing trend data is ignored.
Note: You need to not delete history files (that CitectSCADA creates) from your hard disk while your system is running, as the trend server will attempt to recreate the files and this may cause system performance issues.