To integrate discrete data first fit a cubic spline. That gives you a function you can integrate. Depending on your data, you may want to transform the x data so they are roughly equally spaced before doing the spline, and then adjust the integral value at the end. See "Help", "QuickSheets", "Data Analysis", "Differentiation and Integration of Data Vectors" for more details. If you run into trouble trying this go to this forum: http://collab.mathsoft.com/~mathcad2000 It's where the real action is (this is very much a secondary forum), and unlike this forum it doesn't have ridiculously small file upload limits. If you need to post there, if possible post a worksheet with the data in it. Richard
