If in applying the intercept method for determining average

If in applying the intercept method for determining average grain diameter, one uses only one short line segment, one will probably get different results for different applications of the line. Why is this? How can you insure that there is consistency and a reasonable level of accuracy in the individual measurements?

Solution

The intercept method involves an actual count of the number of grains intercepted by a test line or the number of grain boundary intersections with a test line, per unit length of test line, used to calculate the mean lineal intercept length, ¯. ¯ is used to determine the ASTM grain size number, G. The precision of the method is a function of the number of intercepts or intersections counted. A precision of better than 60.25 grain size units can be attained with a reasonable amount of effort. Results are free of bias; repeatability and reproducibility are less than 60.5 grain size units