If the program is sent using the Program Send button in the Connect Screen, the data is always deleted.
If the program is sent using File Control | Send…, the Preserve Data If No Table Changed option can be selected. If this option is selected, existing data and data table structures on the CR800, CR850, CR1000, and CR3000 (files stored to the CPU) are retained unless one of the following occurs:
To summarize, with newer OSs, any change in the data table structure will delete all the tables on the data logger CPU, regardless of whether or not the program is sent with the File Control | Send… Preserve Data If No Table Changed option selected. If the option was selected, but the data logger was unable to retain the existing data, the Warning: Internal Data Storage Memory Was Re-initialized message appears in Compile Results.
Note: Campbell Scientific recommends collecting data before making any program changes.