Charlie, your question is more around ERG mode than calibrating the Suito. I also have a Suito and have not yet calibrated it!
Read up a bit on ERG mode. But in short… In workouts you are generally put in ERG mode. That means your trainer controls the resistance required for the training segment you are in. The terrain does not control it! So if you are in free ride mode, going downhill feels like going downhill. If you are in ERG mode in a workout, you workout says you must put out x watts and the trainer adjusts to that. So if you put out more/less than that, the trainer compensated the tension. You need not (and preferably must not!) shift. Get your gear and the trainer does the thinking.
Then, there is the spiral of death… GPSLama does best to convey that. But that happens most often when you relax at the end of a block and back off too much, ERG thinks you’re doing low cadence so bumps up the tension… and you can’t get out of that. Some other scenarios as well to get that, but check out his video.
Oh, as for the calibration: there’s a nice thread here (actually started by Shane himself!):
You basically need to ignore the on-screen 37kph wording and simply go up to 55kph. I’m actually planning on doing that just now.
Hope this helps!