It’s common to confuse a Bio 540 with a Misty 540. The difference between them is that one is an off-axis trick while the other is non-inverted spin. In a Bio 5, your head and shoulders are above your hips at all time, whereas in a Misty 5 they are perfectly aligned at horizontal.
That's just the first tip in this How To Bio 540 tutorial. Keep reading for the full progression to learn this trick on the tramp with Tramp Skis, so you can confidently take it to the mountain!