This graph from TiVo Stop||Watch depicts viewership across the course of the Super Bowl on a second-by-second basis. The higher the line, the more viewers. When viewers rewind and watch something multiple times (a "personal instant replay"), this is additive and results in higher total viewership. You will notice most of the viewership spikes in the first half were during commercials (with Doritos "Crystal Ball" spot number one) while during the second half most of the spikes were during crucial game moments (with game winning touchdown number one).