This paper presents Big Ideas of Measurement as a framework of students' thinking about measurement. Drawing from research-based evidence, the framework is a collection of key concepts that students must develop for a robust understanding of measurement and, as such, are key aspects of students' thinking teachers should learn to notice. In a case study with four mathematics teacher educators, this framework was utilized to design an instrument to measure their professional noticing and to analyze the results. Findings provided snapshots of professional noticing of participants with varied expertise in content knowledge and student thinking. Additionally, the choice of artifacts appears to have influenced participants' noticing. [For the complete proceedings, see ED657822.]