Extensions to the Demonstration of Gy’s Formula

Abstract-This paper discusses the fundamental question, "what is an adequate sample size?" in the light of recent developments regarding parameters of Gy’s well-known formula for predicting sampling variance. New understanding of the granulometric factor, g, and the liberation factor, l, had significant impact on the results of calculations involving Gy’s equation. For the granulometric factor, justifications are given as to why nominal comminution size should always be reported as P95 (i.e., the screen size rejecting 95% of the mass). A small but important change in the model to estimate the liberation factor makes the difference between a predictive formula that works or does not. Other parameters and considerations regarding their practical implementation are commented upon in light of the author’s experience.