The document describes a digital diary study conducted to understand how people use fitness trackers. 40 people who used fitness trackers participated in several diary studies over 8 months. The studies involved participants reporting on their tracker usage through short videos and answering questions. Over 170 diary entries were collected. The studies revealed patterns in how participants' tracker usage evolved and the role the trackers played in their health goals. Key findings included that fitness trackers help people learn accurate information about their eating and exercise habits that they previously were unaware of.