Frede 

Thank you very much for the help. Indeed, I am trying to do exactly what you wrote the code for. I may have caused some confusion though as a result of a typographic error in my equation: the result of the equation should EQUAL to the value of 1. I see you have inputted the equation into the function as 1 - (minus) D1/... would you be kind to please provide insights on how that may change the the function is written? By using the equation that way the value of E should be between 1.5 and 6, based on data I have available in a plot, if that helps. 

Greatly appreciate the help

Thanks

Andras 




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