Hi there. I have a problem regarding interpolation between lines. I have to say that I have never done it before and I can't find relevant info on the internet, so I am asking for your help. the graph in question can be found here: http://s9.postimage.org/kmj94nexb/physicsforum.png I do not have any other info other than the X and Y value that I calculate beforehand. When I insert them on the diagram I get a point and if it falls on one of the curves already on the graph, then it's all OK, I read the value of the curve and can proceed with my calculations. Otherwise, I have to interpolate somehow, so the only info I would have is that point I get from the intersection of X and Y, which has to be part of the new (interpolated) curve. For example I have curves 0,8 and 0,9 and I want to get 0,86. I also have to take into consideration the fact that Y is expressed as log. I hope I explained it well enough...thank you.