Frequency of a watch corresponds to the number of alternations made by the balance during one hour. There are two types of measures to assess frequency of one automatic movement:: Hertz and the number of alternations per hour (A/h).
The outrigger is the regulating organ of the watch. It allows to channel the energy received by the anchor and therefore allows the needles to rotate at regular and precise intervals. It is the oscillations made by the rocker that allow the needles to move.
The outrigger receives mechanical energy through the anchor, which allows the anchor to rotate. This is the ICT we hear. At the center of the balance is a spiral which compresses under the effect of rotation of the balance. By relaxing, the spiral forces the balance back: this step is indicated by the TAC we hear. The oscillation is therefore the outward and return movement of the balance, it is therefore composed of 2 alternations.
Frequency is the oscillation number that the balance will perform in 1 second. However, the frequency of one automatic watch in number of alternations per hour or in Hertz. Thus a watch to 28,800 shifts per hour performs 14,400 oscillations in one hour, 240 oscillations per minute and 4 oscillations per second. To expressalternation in Hz the number of oscillations per hour must be divided by 7200. Thus a mechanical watch with a frequency of 28,800 A/h will have a frequency of 4Hz.
The higher a frequency, in other words the more oscillations the balance will make in one second the more precise the watch will be and the more fluid the movement of the hands (in particular of the seconds). However, it should be noted that on some movements, frequency too high may tend to wear the movement prematurely and also reduce the autonomy of the power reserve.
Most of the mechanical watches have of frequencies of 21 600 A/H or 28 800 A/H even if there are watches with frequencies of up to 36 000 alternations in one hour or 10 alternations in one second. On this type of movement, the rhythm of the trotter is smooth, we no longer see increments.