Time, unlike the word tempo, which means speed or pace, is used in music for the metrical divisions or bar-lengths of a piece of music. These are indicated by two numbers at the beginning of a work or at the introduction of a changed time by two numbers that form a time-signature. The higher of the two numbers shows how many beats there are in a bar, while the lower number shows what kind of note it is. In this way a duple time-signature of 2/4 means that each bar consists of two quarter notes or crotchets or their equivalent in notes of shorter or longer duration. An indication of compound time such as 6/8 shows that there are six quavers or eighth notes in each bar, although in faster speeds these will be in two groups of three. Prime higher numbers such as five or seven necessitate asymmetrical groupings of notes.