Until now, we have used the quarter note (crotchet) to represent the value of a beat. Nevertheless, we can indeed use any note value to serve as the beat unit. In time signatures the lower number indicates the kind of note that gets one beat, i.e., quarter note/crotchet (4), half note/minim (2), eighth note/quaver) (8), sixteenth/semiquaver note (16), etc. (see Time or Meter Signatures for more information).
If we use 2 for the bottom number, the half note (minim) will then become the beat unit. We will now illustrate a series of rhythmic formulas written using the time signature of 2/2. Note that the half note (minim) now represents one beat, the quarter note (crotchet) is a half beat and the eighth note (quaver) is a fourth of a beat.
Please visit the Reference Section for more information.