SI Unit Prefixes Now that we know about the SI system and what it provides to the scientist and engineer, we can examine some aspects of actual measurement. The SI system utilizes a standard system of prefixes to the basic units that allow them to be more relevant to and descriptive of relative magnitude. For example, when reading about chemical kinetics, you may encounter the terms “ms” or “ns,” meaning “millisecond” and “nanosecond” respectively. Once you’ve become accustomed to the practice of using the prefixes, you will immediately know that the millisecond is 1/1000 of one second and is 1 million times larger than a nanosecond, which is 1/1000000000 of one second, or 10-9 seconds. Briefly review the basic SI units before you study the prefixes.