If the Archive bit is reset manually or another application resets it Double Image cannot rely on the Archive bit to know if the file changed. Using this method of incremental backup is the default within Double Image.
One key value of using the 'Incremental by Timestamp' option is to allow other backup system to coexist on the same machine and backup the same data, since other software will almost always rely on the Archive bit.
If copying to or from NAS devices not controlled by Windows, then in nearly all cases this option can still be used since Double Image recognizes many non-Windows controlled file systems.
Every file on hard drives and controlled by Windows has its own Archive attribute bit. Traditional backup programs have used this bit for years and still do to determine if a file should be backed up or not. Incremental backups can use the Archive bit to determine which files have changed since the last backup session and only copy those files that have been changed or newly created, whereas full backups copy all files.
As an option, Double Image can also use the Archive bit to determine if a file should be copied during an incremental backup. Although using the Archive bit by Double Image is not the default.
When a file is created or changed, the operating system automatically sets the Archive bit. Typically, this bit remains set until Double Image performs a backup of the file. It is the user's responsibility and decision to reset (clear) the Archive bit during a backup process, if that is even necessary.
To turn off the Archive bit on files being backed up, select File Attribute option named "Reset Archive bit on copied source files".