Hi all, Firstly, hope I'm posting in the right place! I'm working with a company that works with air filters. Without going into specifics etc, I have 4 data points: | x | y | |0mm|21%| |150mm|59.6%| |300mm|83%| |550mm|90%| where x is Filter Height and y is Filtration. (Apologies for bad formatting - I looked but couldn't find the syntax anywhere for posting in a table!) In the title, I've called it 'logarithmic-like' and what I mean by that is that it will not go above 100% (obviously) and looking at the data points, it's got a definite exponential fall off. 21% at 0mm I know sounds wierd, but it's a characteristic of the system which, through laziness and some contractual NDA stuff, I won't go in to. I've used 3 different graph-drawing softwares (Excel, JMP 11 and graph) + WolframAlpha and have come to the conclusion that it isn't possible to alter the curve of a logarithmic plot enough to fit this data. I've also tried flipping the data and an exponential won't fit - x^2 does, but doesn't asymptote at 100%, so isn't really accurate enough. Increasing the power just makes any graphical software peak between the 1st and second points and then rise to the rest. TLDR; I have this data set (above) and I'm attempting to find a line of best fit so that we can design a unit and "know" what filtration it will give. Can anyone help me with a way of finding a formula that fits or a piece of software that will? Thanks in advance!