Surveyor's sector, early 17th century.
© Science Museum / Science & Society Picture Library
An Italian surveyor's sector, engraved 'Adam Heroldt fecit Romae'. The sector was invented independantly by Galileo and Thomas Hook at the end of the 16th century. It primarily measures proportions and can contain lines concerning trigonometry, geometrical drawing and calculations on surfaces and volumes. This instrument is on the stand and is pictured with three later examples.