Since most NumericalValues in the VEC are definitions for technical properties, each NumericalValue can reference a Tolerance. In the example, the specified value of '105.23' has a tolerance of +/- 20.0. Units for NumericalValues are defined globally in the VEC and are reused for each NumericalValue. The example shows the definition of the CompositeUnit Ohm per Kilometre.
This tutorial demonstrates how values with reference systems shall be used. In many cases (e.g. Colors) there is no single way to express a certain literal, but many different ways.
In order to correctly express such values the VEC gives the possibility to define not only the value, but the reference system in which the value is valid, too. This means if I have three valid ways to express the Color “Red”, then I can define and differentiate them. If the value is defined in some standard reference system I will use this (e.g. RGB or RAL for colors). If the value is defined in some company specific reference system, this can be defined, too (see ACME Inc.). For attributes like the “baseColor” of a wire insulation it is possible to define the single value in different reference systems (in the example the color in RGB, RAL and company specific ACME Inc.). However all given values shall refer to the same “real” value.