Using the SI System of Units

Abstract

Abstract SI surpasses previous metric systems in coherence, simplicity, distinction between force and mass, choice of units, and uniformity of usage. Coherence eliminates conversion factors, other than powers of ten, within the system. Through simplification, only seven base units, two supplementary units, fifteen named derived units, and fourteen prefixes are needed to describe the entire system. Introduction of the newton as a unit of force and retention of the kilogram for mass clarifies the difference between the two quantities. Other new units are: pascal for pressure, Siemens for electric conductance and mole for amount of a substance. International agreement minimizes proliferation of specialized units or usage. Adopted conventions include spelling, abbreviations, style, and usage, as well as definitions for the units. Tolerances, rounding of numbers, and elimination of the comma in multidigit numbers assume new significance. Conversion to SI offers a unique opportunity to reduce the number of sizes of many products. Several schemes for metric modularism have been developed for this purpose. In changing from conventional to SI units the key idea is “think metric” rather than use dual dimensioning.