Take the data collected in class for the disks and organize it into a table. One column will be the disk number, the next will be the diameter of the disks (in cm), the next will be the radius (computed by dividing the diameter by 2), and the last will be the circumference (in cm).
Next make a graph of the data. Use graph paper or carefully measured plain paper. Put radius on the horizontal axis and circumference on the vertical axis. Put a data dot for each disk.
Next draw a best-fit straight line (with a ruler) through the data dots. Also make it go through the origin. There are mathematical methods for determining the theoretical best best-fit line, but the eye-ball method works fine for our class.
Now compute the slope of the best-fit line by selecting two widely-spaced points on the line (not data points) and compute the rise/run between the two points. The slopes of straight lines in physics class usually means something important physically. Try to figure out what this particular slope means and compare your computed value with the accepted value (% difference).