.back is RMCProfile coefficient
Key Features: .BACK File Extension
What is an .BACK file?
The back file extension is associated with the RMCProfile program.
The back file contains the coefficients of the shifted Chebyschev polynomial used to fit the background in the GSAS refinement.
This back file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.