In a small room in the 12th century Moyse's Hall in Bury St Edmunds a turtle makes slow, steady revolutions of a shallow pewter dish of water, each turn taking a whole twelve hours to complete — the leaden creature can be placed anywhere in the dish, then after a few curious wiggles will always ‘magically’ return to the perimeter, its nose pointing towards the roman numerals engraved around the rim, and if left undisturbed will then continue on its measured journey around the dish.