WWV also transmits a [//upload.wikimedia.org/wikipedia/commons/c/ce/Tone_440Hz.ogg 440 Hz] tone, a pitch commonly used in music (A440, the musical note A above middle C) during minute 2 of each hour, except for the first hour of the UTC day. Since the 440 Hz tone is only transmitted once per hour, many chart recorders may use this tone to mark off each hour of the day, and likewise, the omission of the 440 Hz tone once per day can be used to mark off each twenty-four-hour period. WWVH transmits the same tone during minute 1 of each hour.