To properly interperet a diffraction image, you need to know the instrument parameters, for example wavelength and sample to detector distance. In some cases these are contained as metadata within the data file, but in most cases they must be determined by the user (using methods in the Calibrate window). The "File" and "User" radio buttons allow you to decide whether you want to use user-determined values (the default) or metadata from the file. The User button will be enabled automatically during the calibration process.)