The reads from the last step are realigned to the reference genome. In this method, SSCS family pairs that have complementary tags will be grouped (family αβ and βα in Figure 2). These reads originate from two complementary strands of DNA. High confidence sequences are selected based on the perfectly matched base calls of each family. The final sequence is called the DCS. True mutations are those that match perfectly between complementary SSCSs. This step filters out remaining errors raised during the first round of PCR amplification or during sample preparation.