I want to create a immutable Scale class in C#.

public sealed class Scale
{
    string _Name;
    string _Description;
    SomeOrderedCollection _ScaleValueDefinitions;
    Unit _Unit

    // properties
    ....
    // methods
    ContainsValue(double value)
    ....

    // constructors
    // all parameters except scalevaluedefinitions are optional
    // for a Scale to be useful atleast 1 ScaleValueDefinition should exist
    public Scale(string name, string description, SomeOrderedCollection scaleValueDefinitions, unit)
    { /* initialize */}
}

so first a ScaleValueDefinition should be represented by to values:

• Value (double)
• Definition (string)

these values are known before the Scale class is created and should be unique. so what is the best approach.

1. create a immutable class ScaleValueDefinition with value and definition as properties and use it in a list.
2. use a dictionary.
3. use another way i didn't think of...

and how to implement it. for option 1. i can use params ScaleValueDefinition[] ValueDefinitions in the constructor, but how to do it for the other options?

and as last at what amount of value's (properties) should i choose one option over the other?