You're talking about those certificates at the seti site? On your certificate page you can change the certnum value in the url to see what the next level is. It doesn't make the certificate, just says you having completed x units yet. The milestones are 100, 250, 500, 1000, 2500, 5000, and 10000. When you try for a level about 10k it displays one for the number of units you've completed.