This document describes the process of constructing and interpreting an interaction matrix to analyze classroom communication events. An observer codes behaviors into categories every 3 seconds, recording serial numbers. These numbers are tabulated into a 10x10 matrix with each number entered as a row-column pair. The matrix cells are then interpreted to calculate ratios like teacher talk percentage and pupil talk percentage. Advantages include providing feedback and being an objective measurement tool, while limitations include taking much time and focusing mainly on teacher behaviors.