Time signatures have a top and a bottom part: the top determines the number of beats and the base determines the form of beat. The time signature is written once after the clef at first of a bit of music unless it adjustments. The way the beats are grouped also depends upon the time signature, but this becomes more apparent as you build up experience of reading music. The tempo tells you how easily the music may be played. Usually, tempo is expressed in beats per minute bpm for a particular beat type. This means 50 crochet beats in a minute. To will let you play at the correct tempo, you could use a metronome. These can be either analogue or digital however the characteristic is the same: it ticks or bleeps on each beat at the set tempo. Metronomes can be especially constructive for orchestras or bands to maintain all and sundry in time with one another. In many pieces the tempo adjustments. This is usually communicated using musical phrases.