Getting feedback from students during a lecture allows teachers to estimate the degree to which concepts have been grasped. If many students seem confused, the professor can review the material again. Clickers allow students to provide answers to questions in real time, helping the teacher to monitor the degree of class understanding. Current models allow for multiple choice, text, and other input.  This video demonstrates the use of clickers to track students’ understanding in Professor Eric Mazur’s introductory physics class.