In musical terminology, tempo (Italian, 'time'; plural tempos, or tempi from the Italian plural) is the speed or pace of a given piece. In classical music, tempo is typically indicated with an instruction at the start of a piece (often using conventional Italian terms) and is usually measured in beats per minute (or bpm). In modern classical compositions, a "metronome mark" in beats per minute may supplement or replace the normal tempo marking, while in modern genres like electronic dance music, tempo will typically simply be stated in BPM. Tempo may be separated from articulation and meter, or these aspects may be indicated along with tempo, all contributing to the overall texture. While the ability to hold a steady tempo is a vital skill for a musical performer, tempo is changeable. Depending on the genre of a piece of music and the performers' interpretation, a piece may be played with slight tempo rubato or drastic variances. In ensembles, the tempo is often indicated by a conductor or by one of the instrumentalists, for instance the drummer. Measurement Although tempo is described or indicated in many different ways, including with a range of words (e.g., "Slowly", "Adagio", and so on), it is typically measured in beats per minute (bpm or BPM). For example, a tempo of 60 beats per minute signifies one beat per second, while a tempo of 120 beats per minute is twice as rapid, signifying two beats every second. The note value of a beat will typically be that indicated by the denominator of the time signature. For instance, in the beat will be a crotchet, or quarter note. This measurement and indication of tempo became increasingly popular during the first half of the 19th century, after Johann Nepomuk Maelzel invented the metronome. Beethoven was one of the first composers to use the metronome; in the 1810s he published metronomic indications for the eight symphonies he had composed up to that time. Instead of beats per minute, some 20th-century classical composers (e.g., Béla Bartók, Alberto Ginastera, and John Cage) specify the total playing time for a piece, from which the performer can derive tempo. With the advent of modern electronics, bpm became an extremely precise measure. Music sequencers use the bpm system to denote tempo. In popular music genres such as electronic dance music, accurate knowledge of a tune's bpm is important to DJs for the purposes of