Dividing the music into bars lets you keep time by counting beats for your head or under your breath. Bar lines vertical lines mark the start and the top of the bar. Time signatures have a top and a bottom part: the tip determines the variety of beats and the base determines the type of beat. The time signature is written once after the clef firstly of a chunk of music unless it adjustments. The way the beats are grouped also depends upon the time signature, but this will become more apparent as you building up event of reading music. The tempo tells you ways simply the music should be played. Usually, tempo is expressed in beats per minute bpm for a specific beat type. This means 50 crochet beats in a minute. To let you play at the right tempo, which you can use a metronome. These can be either analogue or electronic but the characteristic is an analogous: it ticks or bleeps on each beat at the set tempo. Metronomes can be particularly effective for orchestras or bands to maintain everyone in time with one another.