How to measure grain size by linear intercept method?

One of the simplest techniques to estimate an average grain size is the intercept technique. A random straight line is drawn though the micrograph. The number of grain boundaries intersecting the line are counted. The average grain size is found by dividing the number of intersections by the actual line length. Average grain size = 1 / (number of intersections/actual length of the line). where actual line length = measured length divided by magnification.