How do we separate Roughness, Waviness and Form?

In order to separate the three elements, we use filters. On most surface texture measuring instruments we can select either Roughness or Waviness Filters. 

Selecting a Roughness Filter will remove waviness elements, leaving the roughness profile for evaluation. Selecting a Waviness Filter will remove roughness elements, leaving the waviness profile for evaluation. Separating the roughness and waviness is achieved by using filter cut-offs.