Accuracy of Agilent universal error model. As part of the Agilent chip design, a set of 100 oligonuceotide sequences are each represented on the array by 10 separate spots. These are useful for evaluating errors in the estimation of intensity. The vertical axis of each panel shows the mean error, measured across replicate spots, using Agilent's universal error model. The horizontal axis shows the observed standard deviation for the same replicates. Each column shows results for a single array. Some probe to probe differences are captured with the Agilent error model for low intensity probes (blue spots). The bottom row gives a close-up of the high intensity end of each array. For high intensity probes (black), where the level of error is small, the universal error model also predicts low error, however, probe to probe differences are not correlated. These arrays are representative of results seen with Agilent arrays.