Have you ever wondered how people managed before the ruler and the clock were invented? Today, scientists use the metric system of measurement—one based on the meter, kilogram, and second. It is a decimal system. To measure length, normally a ruler is used, to measure mass, normally a balance is chosen, and to measure time normally a clock is chosen. Today, length is measured with meters, mass in kilograms, and time in seconds. This chapter provides some scenarios and explorations to challenge students in designing their own measures.