Randomly is fine. Uptime is being tested randomly as well, but in certain time intervals, for example: every 1 minute, 3 minutes, 5 minutes - to derive to a certain average. How often do you do these tests? As of now it seems like the only test you've done was in October 2008?

Also, you keep avoiding the important question. You told me you use these three uptime software to monitor URLs hosted at those companies: Host-Tracker, Xenos, Uptime Software, but you haven't provided the screenshots or the URLs hosted at tested companies yet. You do use this software, don't you?