There are six pips (short beeps) in total, which occur on each of the 5 seconds leading up to the hour and on the hour itself. Each pip is a 1 kHz tone (about a fifth of a semitone above musical B5) the first five of which last a tenth of a second each, while the final pip lasts half a second. The actual moment when the hour changes – the "on-time marker" – is at the very beginning of the last pip.