> Tuning up a piano from zero is a lot harder than it seems. As the tension on the cast iron frame increases it deforms a bit, enough to de-tune everything you've done up to that point. So the only way to get this done is to tune the whole thing up gradually and to pace yourself so you don't end up overstretching part of the frame or end up in a never ending cycle of de-tunings.

Like tensioning a bicycle wheel! Easy and rewarding process, highly recommended.