This seems to be very confusing to many players. Obviously our music education is being ignored! Just to keep the unknowing from posting something wrong: Low C is below the staff. Third space C is just that. High C is two ledger lines above the staff. Double C is one octave above that. Octaves start with C. This means that Double G is higher than Double C. For the sake of confusion: our double C is merely a high Bb for a flute. There is very LITTLE musical content written for unamplified Double C.