This is confusing. Show a graph with what you have so far. I don't know if you have a plot with 1, 2, or 3 curves on it and what the horizontal variable is and what the vertical dependent variable(s) is/are.
A curve will have many values usually. Let's say x and y are 100 elements long. Do you want all hundred values in the legend? You can use sprintf() to create strings which you can then send into legend(). Alternatively you can use text() to place a string with the value in it next to each marker.
