This document is the primary American National Standard on application of the metric system. It emphasizes use of the International System of Units (SI), which is the modern, internationally accepted metric system. It includes information on SI, a limited list of units recognized for use with SI, and a list of conversion factors, together with general guidance on style and usage. It also lists older "metric" units that shall no longer be used. The word "primary" implies that other metric standards in the United States should be consistent with this document..