and 5, etc.) producing even higher pitches. In practice, however, the uncovering of the holes is not strictly sequential, and the half covering or uncovering of holes is an essential part of recorder technique. Forked fingerings A forked fingering is a fingering in which an open hole has covered holes below it: fingerings for which the uncovering of the holes is not sequential. For example, the fingering 0123 (G5) is not a forked fingering, while 0123 56 (F5) is a forked fingering because the open hole 4 has holes covered below it holes 5 and 6. Forked fingerings allow for smaller adjustments in pitch than the sequential uncovering of holes alone would allow. For example, at the same air speed the fingering 0123 5 sounds higher than 01234 but lower than 0123. Many standard recorder fingerings are forked fingerings. Forked fingerings may also be used to produce microtonal variations in pitch. Forked fingerings have a different harmonic profile from non-forked fingerings, and are generally regarded as having a weaker sound. Forked fingerings that have a different tone color or are slightly sharp or flat can provide so-called "alternate fingerings". For example, the fingering 0123 has a slightly sharper forked variant 012 4567. Partial covering of holes Partial covering of the holes is an essential part of the playing technique of all recorders. This is variously known as "leaking," "shading," "half-holing," and in the context of the thumb hole, "pinching". The primary function of the thumbhole is to serve as an octaving vent. When it is leaked, the first mode of vibration of the air column becomes unstable: i.e., the register changes. In most recorders, this is required for the playing of every note higher than a ninth above the lowest note. The player must adjust the position of the thumb for these notes to sound stable and in tune. The partial opening of the thumbhole may be achieved by sliding or rolling the thumb off the hole, or by bending the thumb at the first knuckle. To partially uncover a covered hole, the player may slide the finger off the hole, bend or roll the finger away from the hole, gently lift the finger from the hole, or a combination of these. To partially cover an open hole, the reverse is possible. Generally speaking, the partial opening of covered fingerholes raises the pitch of the sounding note while the partial