https://doi.org/10.1351/goldbook.G02712

A diagrammatic representation of data on scattering from large particles, obtained at different angles but at the same concentration, constructed by plotting log 10 Δ R θ or log 10 P θ *versus* (sin θ2)2 or q 2 and (usually) used for the evaluation of the radius of gyration. ΔRθ is the excess Rayleigh ratio, P θ the particle scattering function, θ the scattering angle and q the length of the scattering vector.*Source: *

Purple Book, 1^{st} ed., p. 67 (http://old.iupac.org/publications/books/author/metanomski.html)

Purple Book, 1