A base knowledge for a skill is when someone is able to define it,
understands the most important concepts and had at least one
month of practice.
A good knowledge for a skill is when someone is able to define it,
understands all the concepts and had at least one year of practice.
A master for a skill is when someone is able to define it,
understands all the concepts, knows all the details and had
at least seven years of practice.
A master for a skill is when someone is able to define it,
understands all the concepts, knows most of the details and had
at least five years of practice.
An expert for a skill is when someone is able to define it,
understands all the concepts, knows all the details, knows the
history of the skill development, understands what is the future
of the skill, is able to solve any kind of problem related to this
skill and had at least ten years of practice.