Introduction

When you are modeling a physical system, variables generally correspond to physical quantities. A quantity’s value is usually expressed as the product of a number and a unit. If you declare a real variable, you can specify a unit of measure.

The objective of SI units is to make it possible to write equations cleanly, without using conversion factors. We recommend that you use unscaled units when specifying the unit attribute of a real variable.

Users need to enter parameters, and plot variables, in different units. Simcenter Amesim Run supports all the 20 SI prefixes to form decimal multiples and sub-multiples of SI units. A good reference on SI units is what is commonly called the SI brochure, which is published by the Bureau International des Poids et Mesures [1]. The NIST Reference on Constants, Units and Uncertainty [2] gives a good overview. See also [3].

ISO does not specify a formal syntax for unit expressions, but there are strict recommendations.