But my point was more that if it shows 45 (but real is 35), and then you work out a lot and it shows 55 (but real is now around 45), it's still useful even thou

But my point was more that if it shows 45 (but real is 35), and then you work out a lot and it shows 55 (but real is now around 45), it's still useful even though the values are off. As long as the error/bias is the same.