Key Points Every field of science involves taking measurements, understanding them, and communicating them to others. In other words, we all have to speak the same basic language. The SI system, also called the metric system, is used around the world. There are seven basic units in the SI system: the meter (m), the kilogram (kg), the second (s), the kelvin (K), the ampere (A), the mole (mol), and the candela (cd). Key Terms SI system: A series of units that is accepted and used throughout the scientific world.