This document provides information about a math module that focuses on estimating and measuring lengths using rulers and units like centimeters. It explores relating addition and subtraction to length. Key words defined include endpoint, hash mark, estimate, tape diagram, and number line. Prior and subsequent modules are identified. The document encourages asking students estimating questions and measuring household items. It provides examples of relating addition and subtraction to length. A tape diagram is provided as an example of a mathematical model used to represent and solve word problems in the modules.