A graph is drawn to a vertical magnification of 10000 and horizontal magnification of 100, and the areas above and below the datum line are as follows:

Above	150 mm2	80 mm2	170 mm2	40 mm2
Below	80 mm2	60 mm2	150 mm2	120 mm2

The average roughness R_a for sampling length of 0.8 mm will be