What measurement length should I make?

The measurement length is dictated by the numerical value of the cut-off, which itself is dictated by the type of surface under inspection.

Typically, a measurement may consist of a traverse of 6-7 times the cut-off selected. Foe example, 7 cut-offs at 0.8mm = 5.6mm. One or two cut-offs will then be removed according to the filter type and the remaining cut-offs used for assessment. This only applies when measuring roughness.

For measuring waviness or primary profiles, the data length is chosen according to application and the nature of the surface. In general, the data length needs to be sufficient to give a true representation of the texture of the surface.