Fluid trainers and wind trainers don’t have multiple resistance levels – the faster you pedal the more resistance is created by the trainer.
Most magnetic trainers have different resistance levels. With the PowerCurve Software, when you select the model of your magnetic trainer, it will be indicated which level to use. That means the power curve has been measured at that resistance level. Lower resistance levels means an easier resistance level.
The PowerCurve Software will often give you a choice of different resistance levels for the same trainer. Depending on how strong you are, choose a resistance level appropriate for you – so that you don’t spin out on hard intervals.
For an accurate power reading, it is important to not change the resistance level on your trainer once calibrated. To change the resistance change your gearing instead.