AbstractAn existing varying coefficient calibration method for estimating herbage mass from rising plate meter reading was validated using datasets for different years and pastures, and the variation among these in the coefficients of the model was structurally assessed using a linear mixed effects model to develop a versatile calibration equation. The calibration's advantage was confirmed by the lower Akaike's information criterion values in the two current pooled models than those in the model that assumes fixed coefficients throughout the year. While sites affect the degree of gradual change after the reproductive stage in the slope coefficient, years affect the degree of steep change before the reproductive stage in the intercept coefficient. Further, the shift in the levels of both coefficients was detected by site and year.