AN ENGLISH HORARY QUADRANT
the copper-alloy plate engraved with six unequal hour lines, a shadow square with two scales each numbered 4 8 12, a quadrant arc 0-90 divided to 1 and numbered  30 45 60 75 
2in. (51mm.) radius
Davis, J. 'The Chetwode Quadrant: A Medieval Unequal-Hour Instrument', in Bulletin of the British Sundial Society 27 (2015) pp. 2-6.
Read more about the discovery of the Chetwode Quadrant here.
Discover more about the part this object played in the evolution of the modern PC in our Christie’s Digest feature.
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“The finding of the Chetwode example is a great benefit to the history of science.”
This is the oldest English scientific instrument to have been offered for sale at Christie’s. Rather than the system equal hours of 60 minutes throughout the year, the projection for telling the time on this instrument uses unequal hours. This was common in the medieval world when being able to work during daylight was crucial. Unequal hours start at sunrise, midday is 6, and 12 is sunset; thus an hour is longer in the summer than it is in the winter.
Known by its Latin name quadrans vetustissimus, the science behind its projection for the hour lines can be traced back to a Baghdadi manuscript dating to the 9th or 10th century. Almost certainly introduced to Europe via Islamic Spain, they are first recorded in Montpellier in the late 13th century when the design is modified by the Jewish astronomer Profatius (the quadrans novus).The present example was found by a metal detectorist near Chetwode, Buckinghamshire, in 2014 and is an important discovery. Only a handful of comparable instruments are known, one only fragmentary. Of this small group this quadrans vetustissimus is of the earliest form. It has been dated to the 14th century on stylistic grounds, which are backed by metallurgical analysis, although an earlier date is possible.
The Chetwode location, as John Davis points out, raises two interesting possibilities for the astronomical source of the quadrant. Chetwode Priory received its licence from the Bishop of Lincoln Robert de Grosseteste (c. 1175-1253), the scholastic whose scientific writings include treatise on optics and astronomy amongst others. Further, the Priory was founded by Sir Ralph de Norwich, the assumed Bishop of Norwich in 1236. This connection to Norfolk is intriguing because of two 14th/15th century astronomical instruments found by dectectorists there. Whilst we cannot be certain about its origins, the Chetwode quadrant is indeed a great benefit to the history of science.
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