Signed: I. D. F. 1621
While texts provided tables or calculating procedures to determine the range of shot as a function of the gun's elevation, some instrument makers offered similar information. This unusual instrument gives direct readings of distance for use with mortars, with scales for different kinds of shot.
The instrument consists of a foot with a vertical arc and a hinged upper part which carries a sighting tube. The inclination of the upper part is controlled by a screw. When the upper part is raised by turning the screw a pointer moves over the scales on the vertical arc. On one side the pointer is marked for 'fire bombs' ('FEVER K') and on the other for stone shot ('STEIN K'). By an ingenious system of transversal divisions the pointer is able to read each scale down to 10 unit intervals.
In use the instrument would have been longitudinally breech-mounted. It may have been placed with the vertical arc facing the breech and the screw pointing forwards. With the gun horizontal, the target would be sighted through the viewing tube (the direction of which should preferably be reversed from its orientation in figure 53). After estimating or measuring the distance to the target the pointer would be elevated to that distance on the scale, leaving the sighting tube to point downwards. The gun would then be elevated until the target again came in view through the tube.
In addition to acting as a level giving direct readings of range, the instrument probably also served as a more standard sight when the upper part of the instrument was set to zero elevation. The central upright which supports the sighting tube has two pillars on one of which there is a scale from 1 to 10. On the other pillar there is a groove of the same length, suggesting that the upright would once have contained a sliding sight.
Height: 86 mm
Inventory no. 50,613