In terms of changing fitness with a given individual our initial assumption was that yes, as fitness increased the user would need to re-calibrate to properly adjust the system but what the research shows is that these changes are relatively very small compared to other factors at play when using heart rate as the base measurement. In other words, the margin of error when using heart rate as the sole measure of exercise intensity is too great to accurately represent changes in fitness.
In discussions of PowerCal as it relates to fitness, fatigue, dehydration, etc. one can look at the power output relative to other metrics such as speed over the same course or changes in cadence over time. Power output as a performance metric is almost always spoken of in terms of how it relates to the other variables to gain insight to the individual's progress.