60 is the lowest number divisible by the numbers 5,4, and 3. To describe the shortest relative durations between notes, a denominator of 60 is necessary. For instance, the shortest duration, which is three 60ths of a measure, is one 60th shorter than the next shortest duration, which four 60ths.

The shortest duration between any two notes, which is three 60ths of a measure may be described using a denominator of 20. The next shortest duration between two notes - four 60ths of a measure - uses a denominator of 15.