Two ways to find the spring constant - WITH GRAPHS

This is basically a physics lab. How do you find the spring constant for a spring? In the first method, I add masses and measure the stretch. From this, I create a graph of force vs. position. The slope of this line is the spring constant. The second method is where students have trouble. In this case, I put mass on the spring and let it oscillate. From the period, I can make SOME type of linear graph.