I need the simple function for the following set of data. This is a toy version of my data, but the error is persistent in both. To compare with excel, I would just 1) format trendline, 2) display equation and R-squared on chart. I obviously tried to use a nls and wanted to use the self startup function SSasymp rm(list=ls()) t <- c( 0,.1,.2,.7,.4,.5,.6,1,.8,.4,1.2,1.3,1.4,1.5,1.6, 1.6,1.7,1.8,1.9,2.0, 3,6,11) y<-c(2,3.5,3.01,3.09,3,3.25,3.36,3.49,3.64, 3.81, 4.44, 4.69, 4.96, 5.25, 6, 6.1, 5.89, 6.24, 6.61, 7.00, 12.00, 39, 124.00) plot(y~t ,xlab="t", ylab="y") model<-nls(y~SSasymp(t,a,b)) summary(model) Thanks in advance, keith -- M. Keith Cox, Ph.D. Alaska NOAA Fisheries, National Marine Fisheries Service Auke Bay Laboratories 17109 Pt. Lena Loop Rd. Juneau, AK 99801 Keith.Cox@noaa.gov marlinkcox@gmail.com U.S. (907) 789-6603 [[alternative HTML version deleted]]