17th century

  Fig. 92          Fig. 93

A brass rule, with a 12-inch scale on one bevelled edge, divided to 0.1, a protractor and a variety of fortification diagrams. The protractor is not for measuring angles in degrees, but is engraved with lines marked 12-4-12, with line 4 in the right-angle position. These lines are for setting out regular polygons with the indicated number of sides. Both sides of the rule have plans of fortifications with the geometry of their construction given in accompanying tables, one side marked 'INTRORSVM' (towards the inside), the other 'EXTRORSVM' (towards the outside).

Length: 304 mm

Inventory no. 45,283