Process capability analysis was performed on newly purchased Zellweger model 900-Automatic High Volume Instruments with dual color heads in 1994 and 1995 using the same methodology for the fiber properties of micronaire, strength, length and uniformity. The results from the two years were compared. Improvements in the C_p and C_pk indices and in the ratio of the C_pk index to the C_p index were seen despite little or no decreases in measurement variability. This is due to a decrease in the variability between instruments.