An unsolved problem in qualitative physics is generating a qualitative understanding of how a physical system is behaving from raw data, especially numerical data taken across time, to reveal changing internal state. Yet providing this ability to "read gauges" is a critical step towards building the next generation of intelligent computer-aided engineering systems and allowing robots to work in unconstrained envirionments. This paper presents a theory to solve this problem. Importantly, the theory is domain independent and will work with any system of qualitative physics. It requires only a qualitative description of the domain capable of supporting envisioning and domain-specific techniques for providing an initial qualitative description of numerical measurements. The theory has been fully implemented, and an extended example using Qualitative Process theory is presented.