Hi

I'm trying to create a protocol to fit some ELISA data.  In the past my scientists have done this in Excel and I want to automate the process using PP.  They generate a sigmoid standard curve by plotting log(concentration) on the x-axis, against Abs450 on the y-axis and fit the data using a 4 parameter logistic (4-PL) model and Solver.  The 4-PL equation can be easily rearranged to work out the concentration from the absorbance of each well (it's a plate based assay).  When I use the sigmoid fit in the Least Squares Fit component, and give it estimated values of the four parameters, the standard curve fits correctly, however the equation being fit does not appear to be in the normal 4-PL form of y = D + (A-D) / (1 + (x/C)^B) (1) and does not rearrange easily (for me ).

I had a look at the dose response components and they seem to fit equ 1 above instead of the model used in the least squares component, however when I feed in my standard curve data and plot the data, the fitted curve is wrong. 

The strange thing is, when I look at the data record tree for the output of each of the fitting components, they arrive at the same coefficients for each parameter, but as you will see from the attached protocol, the fit is reversed in the Dose Response Fit output .  Obviously if the coefficients are correct, I should be able use them, but I want to plot the fit of the standard curve so the scientists can judge the quality of the assay.

On a related note, does anyone know what's going on with PP8.0 and image charts?  I can't seem to get titles and axis labels to appear correctly - I get little boxed where the characters should be - but draw a flash chart and my labels come back?

Thanks for your help - I'm probably missing something really obvious!

Hassan