system, which simplified fingering somewhat. The most substantial departures from Boehm's original description are the universal elimination of the "crutch" for the left hand and almost universal adoption of Briccialdi's thumb key mechanism and a closed-standing G key over an additional G tone hole. Boehm's key system, with minor variations, remains regarded as the most effective system of any modern woodwind, allowing trained instrumentalists to perform with facility and extraordinary velocity and brilliance in all keys. The modern flute has three octaves plus C7–C7–D7 in the fourth octave. Many modern composers used the high D7; while such extremes are not commonly used, the modern flute can perform up to an F7 in its fourth octave. 19th-century variants The Meyer flute was a popular flute in the mid 19th century. Including and derived from the instruments built by H.F. Meyer from 1850 to the late 1890s, it could have up to 12 keys and was built with head joints of either metal-lined ivory or wood. The final form was a combination of a traditional keyed flute and the Viennese flute, and became the most common throughout Europe and America. This form had 12 keys, a body of wood, a head joint of metal and ivory, and was common at the end of the century. Quite at the opposite end of the spectrum, in terms of the complexity of the key system developed by Boehm, was the Giorgi flute, an advanced form of the ancient holed flute. Patented in 1897, the Giorgi flute was designed without any mechanical keys, though the patent allows for the addition of keys as options. Giorgi enabled the performer to play equally true in all musical keys, as does the Boehm system. Giorgi flutes are now rarities, found in museums and private collections. The underlying principles of both flute patterns are virtually identical, with tone holes spaced as required to produce a fully chromatic scale. The player, by opening and closing holes, adjusts the effective length of the tube, and thus the rate of oscillation, which defines the audible pitch. Modified Boehm flute In the 1950s, Albert Cooper modified the Boehm flute to make playing modern music easier. The flute was tuned to A440, and the embouchure hole was cut in a new way to change the timbre. These flutes became the most used flutes by professionals and amateurs. In the 1980s, Johan Brögger modified the Boehm