I've got Tacx Flow ergo trainer that I love. Someone had posted that they are using a Tacx Basic but don't know how to do the calibration.
I was just googling a little and haven't found the exact protocol so the person should spend some more time searching for the step-by-step. It seems that Tacx has their own forum where you could post a question. There are also some threads on other cycling forums.
The basic strategy is to pump your tires up to the same pressure every time. Get up to a set speed (25mph?) then stop pedaling. Time how long it takes for the wheel to stop turning. This is called a roll down calibration.
The FLOW which was the next training up in their model line does this automatically. You pedal until it tells you to stop. Then it countsdown automatically and lets you know if your resistance is set too high or too low. On the basic you have do to the know when to stop pedaling and counting manually.
Anyway, those with a basic should take some time and look for the exact protocol. Let me know if you find it and I'll post it here for others.
calibration is really important. While the Tacx might not provide exact power numbers that are identical to a power tap or an SRM I do think that when calibrated they numbers are very repeatable which is essential for tracking your training and setting interval intensity.