The data-processing ability of double wavelength/double beam spectrophotometer has been greatly enhanced by connecting it to a computer and designing new software. Formerly, the instrument relied on an old recorder to plot curve on a special-designed recording paper and had poor data-processing ability: user had to determine manually the abscissa and ordinate for any data point in the curve with a ruler, which limited its use in biological studies, especially in kinetic analysis. Currently a computer and a software packet designed are applied to it, which leads to the following several distinct advantages over the old type: sampling and storing data by computer, showing more than one curve simultaneously on the screen, showing the value of data points, determining the positions of peaks automatically, smoothing curves, zooming in or zooming out graph, printing graph with a HP Laser Jet. The structure of the new system is introduced here, based on which the effect of phosphatidylethanolamine content on the Ca²⁺ uptake of Ca²⁺-ATPase is studied.