Fig. 4. Measured (symbols) and simulated (lines) leaf weight ratio (LWR) of timothy grown at Nappan in 1997 and 1998. The parameter "a" represents intercept, and the parameter "b" represents the slope of the linear regression between simulated and measured values. RMSE, root mean square error of the prediction; RMSEn, normalized RMSE, calculated as RMSE divided by the average value of the attribute.