The number of repetitions per unit time is given by the reciprocal of the:

1. Period and frequency describe the same repetition from two sides. 2. One counts time per cycle and the other cycles per time. 3. The reciprocal of T gives the number of repetitions per unit time. 4. So frequency is the reciprocal of the period. _Source: syllabus Physics Part II, Ch 13 'Oscillations'_