I'm just setting up a risk management for a project, and I have to admit, that I'm not used to it. That's my table so far.

|Identification         |Analysis            |Prevention           |Final Risk |
|ID|Name |Desc |Reasons |Possibility |Impact |CounterM |Monitoring |           |   

I will give scores for the Possibility of an occurrence and the Impact on occurrence. Placing the risk on a matrix, will show me the raw severity of the risk. I also will define Countermeasurments in case of an occurrence and Monitoring methods to avoid an occurrence. Both of them, especially Countermeasure will logically influence the Total Risk. I think about a formula like

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Is this reasonable? How would I calculate the Countermeasure value?