RA-values measure the depth in the base structure and reveals properties of the base.
The ski base has a complex structure with small nuances at micrometer level. The structures reveal a near unlimited amount of detail. Trying to understand how much each tiny nuance impacts glide properties can be overwhelming. We therefore summarize the properties of the microstructure into some key values.
In the world of Nordic skiing, a commonly uses parameter is the RA-value. RA stands for Roughness Average and indicates the depth of the structure on the micrometer level. RA-values are measured with a needle that moves across a surface in a straight line. The needle catches the depth of the structure, and the result is a graph showing the elevation profile.
The RA-value measures roughness along a single 1-dimensional line. Therefore, the direction in which we are measuring is crucial. The structure in a ski base is typically set as lines in the direction of the length of the ski. Therefore, there will naturally be more transversal roughness compared to directional roughness. This is why we measure the RA-value along the width of the ski. We always measure two different places and take the average number to get better quality of the measurements.
The RA-values are summarizing the properties of the ski base with a single number. Obviously, a single number cannot describe the vast amount of details in a ski base. But because the surface of the base of the ski has very structured details, the RA-value says a suprising amount about the base properties. Through the RA-value, we can easily reveal mistakes in the combination of grind and ski properties.