on Mar 9, 2017
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Their use continued through the early 19th century, when they were supplanted by reliable mechanical timepieces, and by other advances in marine navigation
Over time, the later progress in the art of glassblowing allowed them to be made in a single piece
[7][8] By the 8th century it is mentioned by a monk named Luitprand, who served at the cathedral in Chartres, France
[11] Use of the marine sandglass has been recorded since the 14th century
[2][3] Filled with the amount of sand suitable for measuring a lapse of half an hour, each time the sand emptied was also called a "glass"
[2][3] The marine sandglass was critical for maritime navigation before the 19th century
[2][3] At the beginning of that century it became possible to navigate by the lunar distances
[2][3] The parallel use of relative time measurements at sea, and time measurement by mechanical clocks on land continued from at least 1350 to 1805, i.e., for more than 450 years
[2][3] The design of the glass affected its accuracy in time measurement
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