The precise spectral overlap between the four dyes is measured by running DNA fragments labeled with each of the dyes in a special calibration run on the ABI PRISM® Genetic Analyzer. These dye-labeled DNA fragments are called matrix standards. The Data Utility software then analyzes the data from the matrix standard samples and creates a matrix file. These numbers are normalized fluorescence intensities and represent a mathematical description of the spectral overlap that is observed between the dyes. The matrix files in an instrument file are used for specific types of chemistry, and provide information to the Sequencing Analysis software to allow it to correct for spectral overlap.