I'm modelling a variable output Y which has a value of 1 at x=0. I've noticed that in the system I'm modelling, as x increases, y increases at an exponentially decreasing rate, up until a limit of around 1.53. I view this as changes in x causing the Y value to increase by a max of 53%. The only problem is I've been working at it but I don't know where to begin in modelling a function with such a limit. Can anyone think of a solution? Thanks!