Very Popular Since The 19Th Century. At That Time, Electric Light And Luminous Dials And Hands Had Not Yet Been Invented. This Complication Sounds A Tone To Indicate The Hours By An Internal Mechanism. Very popular since the 19th century. At that time, electric light and luminous dials and hands had not yet been invented. This complication sounds a tone to indicate the hours by an internal mechanism. Various types of repeater designs have been made. 1) A minute repeater sounds a low tone for each hour, two tones for each quarter hour and one high tone for each minute after the quarter hour. 2) A quarter repeater sounds one low tone for the hours and a double (high tone followed by a low tone) for the quarters. 3) A five-minute repeater sounds a low tone for the hours and five minute intervals after the hour on a higher tone.