ABSTRACT
The dimensions of a quantity identify the physical character of that quantity, for example, force, mass, length, time (t), temperature, electric charge, etc. Several different sets of units are in use in both scientific and engineering systems of dimensions. These can be classified as either metric or English. Although the internationally accepted standard is the SI scientific system, the English engineering units are still very common in the United States and will probably remain so for the foreseeable future. Physical laws, theories, empirical relations, etc., are expressed by equations that relate the various variables and parameters. Ordinarily, numerical quantities that appear in equations that have a theoretical basis are dimensionless and hence "universal." The conclusion that dimensionless numerical values are universal is valid only if a consistent system of the units is used for all the quantities in a given expression.
