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Guinier analysis in the ATSAS software package for analysis of biological SAXS data:
[note: this Guide is for ATSAS 3.2.1 on mac - there may be minor differences between operation systems and ATSAS versions.]

• Go to the ATSAS download site, and download ATSAS (free for academic users and students. You need to make an user, but this is free and fast).
• Open Primus (should be in you app folder after installation). Primus is a GUI for ATSAS and has many great options.
• Load the data into Primus. Go to the Analysis tab. Press the bottom "Radius of Gyration". Press "Next".
• You will then see a Guinier plot as well as values for $R_g$ and $d_\mathrm{max}$. You may adjust the Guinier region by adjusting the "Range". The parameter Type determines the maximum value of $qR_g$ to include. For globular particles like lysozyme, this should be ca 1.3.
• Congratulations, you have done a Guinier analysis!