# Calculating Full-width Half-max (fwhm)

Jun 27, 2007calculate the full-width half-max of a peak in data? My chart (gray value vs. pixels) essentially looks like a letter M. What I've tried is finding the max of each peak, dividing that by two, and then using vlookup to find the corresponding pixel values on each side of the peak. But, since vlookup does not work for descending values, I cannot find the half-max value on the right side of each peak.