This is a common experience among education researchers: we notice a surprising instructional move enacted by a teacher. After deeper reflection, we ask, "How many other teachers in Singapore do this?" In this paper, we describe an instrument we designed that is part of the resource needed to answer such questions. [This paper is the third in a symposium of four papers. For the first paper "A Study of School Mathematics Curriculum Enacted by Teachers in Singapore Secondary Schools," see ED604245. For the second paper "Instructional Strategies Adopted by Experienced Secondary Teachers When Enacting the Singapore School Mathematics Curriculum," see ED604247. For the fourth paper "Singapore Secondary Mathematics Pedagogy: The DSR DNA," see ED604249.]