are found mostly in high-end flutes because of gold's cost. Mechanical options B thumb keyThe B thumb key (invented and pioneered by Briccialdi) is considered standard today. Open hole keys versus plateau keys Open-hole "French model" flutes have circular holes in the centers of five of the keys. These holes are covered by the fingertips when the keys are depressed. Open-hole flutes are frequently chosen by concert-level flautists, although this preference is less prevalent in Germany, Italy, and Eastern Europe. Students may use temporary plugs to cover the holes until they can reliably cover the holes with the fingertips. Some flautists claim that open-hole keys permit louder and clearer sound projection in the lower register. Open-hole keys are needed for traditional Celtic music and other ethnic styles and some modern concert pieces that require harmonic overtones or "breathy" sounds. They can also facilitate alternate fingerings, "extended techniques" such as quarter-tones, glissando, and multiphonics. Closed holes (plateau keys) permit a more relaxed hand position for some flautists, which can help their playing. Offset G versus in-line G keys All of Boehm's original models had offset G keys, which are mechanically simpler, and permit a more relaxed hand position, especially for flautists with small hands. Some players prefer the hand position of the in-line G. For many years there was a misperception that inline G was for "professional" flutes while offset G was for "student" models, but this stereotype has been largely debunked. Split E The split E modification makes the third octave E (E6) easier to play for some flautists. A less expensive option is the "low G insert". B foot The B foot extends the range of the flute down one semitone to B3 (the B below middle C). Gizmo key Some flutes with a B foot have a "gizmo key": a device that allows closure of the B tone hole independently of the C and C keys. The gizmo key makes C7 easier to play. Trill keys The three standard trill keys permit rapid alternation between two notes with disparate standard fingerings: lowest, middle, and highest trill keys ease C–D, C–D, and B–A, respectively. Some higher notes (third-octave B and B and most fourth-octave notes) also require use of the two lower trill keys. A fourth so-called C trill key is an increasingly popular option available on many flutes. It is named after one of its uses, to ease