 The main factors related to error are the presence of homopolymers, position in the sequence, size of the sequence and spatial localization in BT plates for insertion and eletion errors. No single variable can account for the error rate distribution, but most of the variation is explained by the combination of all seven variables. The pattern identified here calls for the use of internal controls and error-correcting base callers. This article was authored by Miloza Tibor, Ferreira Stephanie, Technicolas, and others.