| Name and Model Number | Lerebours Brass 17-cm Military Sector |
| Country of Origin | England |
| Date of Manufacture | c.1820-26 |
| Front Scales | Special sector and gunnery scales |
| Back Scales | Special sector and gunnery scales |
| Scale Length | Sector length 17-cm (34-cm unfolded) |
| Type of Rule | Rule |
| Construction | Brass; 2-equal length legs with hinge |
| Area of Use | Military |
| Comment | The "Sector" is a calculating instrument attributed to Galileo & others in the late 1500s. It is made up of two rules of equal length hinged together so that it lays flat and the inside long edges meet when the sector is closed. Some scales radiate from the hinge point, and others run parallel to the long edges. The Sector is used partially folded to proportionally size different shapes, making measurements from scales on one leg to matching scales on the other leg with a pair of dividers. This example also has gunnery scales for determining the weight (of cannon balls?) for different materials. The scales are not logarithmic. This example made by Lerebours in Paris, France, c.1790. |
| Rarity | RRRR |
| Donor | Collection of Ed Chamberlain |
| Match Number | 181 |
| Thumbnail (Click Picture for Details) |  |
| In conjunction with our 'donors' we assign a rarity rating to each item, based on the system devised by Herman van Herwijnen |
| (1929 - 2004), renowned Dutch collector, author, and creator of Herman's Archive, a collection of 5,000 slide rule images on CD. |
| • RR = Rare - 1 of 25 collectors has one; it may take a year to find an example in the marketplace. |
| • RRR = Very Rare - only a few known to collectors; may be several years before it comes up for sale. |
| • RRRR = Extremely Rare - a museum piece; unlikely that an example will come up for sale. |