This paper considers three horary quadrants of strikingly similar design and underlying mode of conception. Two are dated, 1398 and 1399, while the third, undated instrument can now be dated for the first time with some certainty to 1400. The parameters used in their construction are analysed, and the latitude for which they were made is elucidated. This shows that all three were made for use in London or southern England. One of the three, dated 1399, has previously been attributed (...) to the patronage of Richard II, King of England, by virtue of the badge decorating the quadrant. The badge on the second quadrant, dated 1398, for a long time also associated with Richard II, has now been established to have been used by Richard's half brother, John Holland, Duke of Exeter. The third quadrant undoubtedlybelongs to the group, but cannot be assigned to the patronage of any individual. (shrink)