The Material Ratio Curve (MRC) is sometimes referred to by different names including:

 

Abbot-Firestone curve

Abbot-curve

Bearing ratio curve

Bearing area curve

 

These are all the same.  The material ratio curve is the integral of the amplitude distribution function (ADF/Surface Histogram). It is a cumulative probability distribution. It is a measure of the material to air ratio expressed as a percentage at a particular depth below the highest peak in the surface. At the highest peak, the material to air ratio is 0%, where the material to air ratio at the deepest valley is 100%.  The Sk, Spk, Svk, and material ratio parameters are computed directly from this curve.

 

 

There are three options available for viewing the height distribution data.  View the material ratio curve only, view the material ratio curve along with the ADF curve, or view the ADF alone.  When viewing the MRC, a cursor can be displayed.  The cursor can be dragged back and forth along the MRC to compute the material ratio at a specific depth of the surface.