Hi, I'm doing my GCSE Physics Coursework, and I'm doing cooling curves. To find the rate of cooling at any temperature, it is neccesarry to draw a tengent to that certain temperature, and then find the gradient of the tangent. Does anyone know how to do this in excel? Because I've done the graph in excel, doing it manually (although fine) is harder, as I don't know precisely where the points are (like 55.2). I know it is possible because I've found a page mentioning it on the internet, yet no instructions. My cosuin has told me that he found a site with instructions but they were really complicated, and that's not for me (he doesn't remember where he found the sight, it was a couple of yrs ago). Anyone help?