Place the Trebuchet on the floor with a clear projectile landing area. Weigh 12 mass plates and hang them on the Trebuchet. Make a series of clay projectiles of a known mass. Begin with 1.0 gram, 2.0 gram, 3.0 gram, up to 10.0 grams. Set up the graph paper to record the data by drawing an x and y-axis on the paper. Label the x-axis as weight of the projectile and label points every 1/2". Label the y-axis as distance and label points in meters every 1/2". Label the chart as "Counterweight" and the mass of the 12 mass plates.
Launch the 1.0-gram projectile and measure the distance thrown. Record this on the graph. Retrieve the 1.0-gram projectile and repeat the launch and measurement. Launch the 1.0-gram projectile again so there are three points on the graph. Change to the 2.0-gram projectile. Launch it three times and record the data points. Continue this procedure until all projectile have been launched three times.
At each projectile weight, approximate the average of the three throws and make a dot larger than the marks made for each throw. Do this for each weight of projectile. Connect the large dots with a line to make a line graph of the results.