Gy's sampling theory is a theory about the sampling of materials, developed by Pierre Gy from the 1950s to beginning 2000s in articles and books including:(1960) Sampling nomogram (1979) Sampling of particulate materials; theory and practice (1982) Sampling of particulate materials; theory and practice; 2nd edition (1992) Sampling of Heterogeneous and Dynamic Material Systems: Theories of Heterogeneity, Sampling and Homogenizing (1998) Sampling for Analytical Purposes