Here we can measure peak asymmetry in one of two ways as shown here.The Tailing Factor, measured at 5% of the peak height, is largely used in the pharmaceutical industry. The Asymmetry Factor measured at 10% of the peak height is most often used in non-pharmaceutical analyses.
In most cases, the Asymmetry Factor and Tailing Factor will be roughly the same (although rarely exactly equal). Values should normally fall between 1.0 and 1.5 for a new column and the conditions of the test chromatogram. Less symmetrical peaks are often observed under actual running conditions with "real" samples, but any increase in peak tailing is a symptom of a problem that should be fixed.
http://www.chem.agilent.com/Library/Support/Documents/a10424.pdf
