Instead of obtaining the whole distribution with a sophisticated instrument, a variance estimate for the fibre diameter may be determined - using weight - biased samples obtained from specially designed test method (previously reported in part 1) - with the existing air flow apparatus. The coefficients of variation of diameters estimated by the new methods, empirical and theorytical under the normality assumption of the fibre diameter, are in excellent agreement with the comparable values obtained by the projection microscope. For the purpose of increasing the precision and accuracy of fineness test with the air flow apparatus, a spacer technique has been successfully adopted.