Hi Matt, Here is the session file for the UO2 fitting. The screenshot blow shows what the customized variables look like right before saving this session. Please feel free to let me know if you need any extra information. Best, Juejing Liu Guo Group Materials Science and Engineering program Alexandra Navrotsky Institute for Experimental Thermodynamics Washington State University Pullman, WA 99164-4630 Office: Fulmer Hall, Room 630 Phone: 208-206-7304