Here is my problem. Let's say you have a graph with 3 data points, (0,0), (10,10), and (30,20). These three points are connected by straight lines, NOT a trend line. Now I want to be able to find the Y value for any X value that I input. For example in the hypothetical graph above if I input 5 for an X value, the Y value should be 5. Even though (5,5) is not a data point, by looking at the straight line between (0,0) and (10,10) one could see that when X=5, Y=5. Basically what I have is a bunch of values for a bunch of different times. The times are random, like 0, 17, 55, 80, and each random time has a Y value. However i want to be able to see the Y values for times 10, 20, 30, 40, 50 etc. Is there an easy way to do this?