Chromatograms can be binned on the basis of their quality scores into Low, Medium or High quality bins. The parameters for each of these bins are set under Tools → Preferences → Sequencing (see section 1.2.1 for more information). To see the bin for a trace, add the Bin column to the document table by going to View → Table Columns. You can also view the percentage of bases that are low, medium or high quality by adding LQ%, MQ%, and HQ% columns to the document table.