Friends: I have a brief, somewhat embarrassing question: is there a standard equation for calculating the uncertainty in one's zeta, and if so what is the citation? Thanks, Rich ______________________________ Dr. Richard Ketcham Research Scientist Manager, High-Resolution X-Ray Computed Tomography Facility Jackson School of Geosciences 1 University Station, C-1100 University of Texas at Austin Austin, TX 78712-0254 Office: (512) 471-6942 Lab: (512) 471-0260 Fax: (512) 471-9425 Email: [log in to unmask] http://www.ctlab.geo.utexas.edu