Mass dial

A tide dial, also known as a mass or scratch dial, is a sundial marked with the canonical hours rather than or in addition to the standard hours of daylight. Such sundials were particularly common between the 7th and 14th centuries in Europe, at which point they began to be replaced by mechanical clocks. There are more than 3,000 surviving tide dials in England and at least 1,500 in France.

The name tide dial preserves the Old English term , used for hours and canonical hours prior to the Norman Conquest of England, after which the Norman French hour gradually replaced it. The actual Old English name for sundials was or "day-marker".

Jews long recited prayers at fixed times of day. Psalm 119 in particular mentions praising God seven times a day, and the apostles Peter and John are mentioned attending afternoon prayers. Christian communities initially followed numerous local traditions with regard to prayer, but Charlemagne compelled his subjects to follow the Roman liturgy and his son Louis the Pious imposed the Rule of St Benedict upon their religious communities. The canonical hours adopted by Benedict and imposed by the Frankish kings were the Night Office (Nocturns) said in the wee hours, the Morning Office (Matins or Lauds) in the dawn just prior to sunrise, Prime after the 1st hour of sunlight, Terce at the 3rd, Sext at the 6th, Nones at the 9th,Vespers at sunset, and Compline after a period of rest and reading. Monks were called to these hours by their abbot or by the ringing of the church bell, with the time between services organized in reading the Bible or other religious texts, in manual labor, or in sleep.

...
Wikipedia