Hi all; I have a function with calculate a result as fallow: res = (50.0 * (1.0 + sin((x / 23.0 - (x / 23)) * 360.0 * pi / 180.0))) ## and x is the variable which vary on each call. know I need the have the slope of the curve as each point! :-/ is there any method out? or any fast idea to let me find it out? tnx Regards, Ali R. Taleghani +1(424) 279-4548 @linkedIn <http://ir.linkedin.com/in/taleghani>