The cost in Resolve Points to improve a skill by 1 rank is equal to the bonus to which it is being raised. Thus, the costs are as follows.
Unskilled (+0) to Amateur (+1): 1
Amateur (+1) to Competent (+2): 2
Competent (+2) to Professional (+3): 3
Professional (+3) to Expert (+4): 4
Expert (+4) to Master (+5): 5
Master (+5) to Legendary (+6): 6
So, for example, raising a skill from Unskilled (+0) to Amateur (+1) costs 1 Resolve Point; from Unskilled to Competent (+2) costs 3 points; from Unskilled to Professional (+3) costs 6 points.
Contractors may raise skills no higher than Master. Harbingers and many supernatural creatures can reach Legendary level; normal humans cannot.
It is not possible for a new character to start with a skill higher than Professional. If you are a normal human with a skill at Expert or Master, you will never become a Contractor. After all, if the Harbingers were interested in you, they would have recruited you before you became so skilled. Harbingers don't dawdle.
Skills may only be trained during downtime. It is not possible to improve a skill during a Contract or a Side Game.
