Within-slide normalization of rice GeneChips. M was the log intensity ratio and A was the average log intensity for a dot in the plot. Each point represented the expression pattern of a probe-set in the plot. The horizontal red lines represented the theoretical median of the global M-values. The continuous blue curves indicated the global trend line, as estimated by LOWESS regression. (Left) MA-plot before within-slide normalization; (Right) MA-plot after within-slide normalization.