The modern orchestral standard of using soprano clarinets in B and A has to do partly with the history of the instrument and partly with acoustics, aesthetics, and economics. Before about 1800, due to the lack of airtight pads "(see History)", practical woodwinds could have only a few keys to control accidentals (notes outside their diatonic home scales). The low (chalumeau) register of the clarinet spans a twelfth (an octave plus a perfect fifth), so the clarinet needs keys/holes to produce all nineteen notes in this range. This involves more keywork than on instruments that "overblow" at the octave—oboes, flutes, bassoons, and saxophones, for example, which need only twelve notes before overblowing. Clarinets with few keys cannot therefore easily play chromatically, limiting any such instrument to a few closely related keys. For example, an eighteenth-century clarinet in C could be played in F, C, and G (and their relative minors) with good intonation, but with progressive difficulty and poorer intonation as the key moved away from this range. In contrast, for octave-overblowing instruments, an instrument in C with few keys could much more readily be played in any key. This problem was overcome by using three clarinets—in A, B, and C—so that early 19th-century music, which rarely strayed into the remote keys (five or six sharps or flats), could be played as follows: music in 5 to 2 sharps (B major to D major concert pitch) on A clarinet (D major to F major for the player), music in 1 sharp to 1 flat (G to F) on C clarinet, and music in 2 flats to 4 flats (B to A) on the B clarinet (C to B for the clarinetist). Difficult key signatures and numerous accidentals were thus largely avoided.