Tutorials:-Working with Power MILL "PART IV" Finish Machining Strategies.
Finishing strategies machine the actual component form and where applicable, follow on from the Area Clearance operation. Suitable values are required to control the accuracy and amount of excess material to be left on a component by a tool path. The parameters used for this purpose are called Thickness and Tolerance
Thickness is the amount of extra material specified to remain on the work-piece after machining. This can be applied generally (as shown), or independently as separate Radial and Axial values within the machining options.
It is also possible to assign additional Thickness values to groups of Surfaces on the actual model.
Tolerance controls the accuracy to which the cutter path follows the shape of the work-piece. For roughing a Coarse tolerance can be used but for finishing a Fine tolerance must be used.
Note where the Thickness value is greater than 0 it should always be greater than the tolerance value
First image showing the Coarse tolerance and the second one is showing the Fine tolerance.