Fields

When your variables are defined Private they are only visible inside the class.
When your variables are defined Private they should only be modified from inside a Property Get or Property Let procedure.
These are often used for internal calculations.

Private dbInternal_Calculation As Double 

You should use Properties to expose these values outside of the class if you need to.
The value of your properties can be saved using private variables which are called fields.

Private field_sDepartment As String 
Private field_dbNormalHours As Double 
Private field_dbOvertimeHours As Double