Stadimeter

A stadimeter is an optical device used to estimate the range to an object. To use it, you must already know the height of that object. The device works by measuring the angle between the top and bottom of the object. This measurement is taken as the object is observed through the tool. Because it uses physical parts to solve mathematical problems, it is considered a type of analog computer.

Using the device involves a specific sequence of steps to find the distance. First, the operator must set the known height of the target object. In many models, this is done by adjusting a knob. Next, the operator looks through the device at the target. They adjust the parts until the top and bottom of the object align perfectly. Finally, the operator reads the calculated range from the edge of a knob. A small magnifying lens often helps the user see this reading clearly.

This tool belongs to a group of instruments called optical rangefinders. It is very similar to a sextant. A sextant uses mirrors to measure an angle between two points. However, the stadimeter is different because it allows the user to dial in a specific height. One major advantage of the stadimeter is its size. It does not require a large, bulky instrument to function. This makes it ideal for handheld use or for installation inside a submarine periscope.

The history of the stadimeter began with Bradley Allen Fiske. He was an officer in the United States Navy who lived from 1854 to 1942. He originally designed the device for gunnery purposes. He conducted the first sea tests for his invention in 1895. These tests revealed that the tool was useful for more than just combat. It proved equally helpful for fleet sailing and for general navigation.

Following these successful tests, the United States Navy Bureau of Ships began ordering handheld versions. These orders started shortly after the device was developed in the late 1890s. By the early 1900s, the stadimeter became standard equipment for navigation officers. It was used alongside other essential tools like the sextant, the spyglass, and the maneuvering board. It was also used with the parallel motion protractor to help manage warships.

During World War II, engineers developed a more advanced version known as the Mark 5. The Mark 5 Mod 0 was produced in 1942 by Schick Inc. of Stamford, Connecticut. This version changed how the height was set to make it more efficient. Older models used a linear screw worm drive to set the object's height. This screw drive was quite slow to move. The Mark 5 replaced this with a single pivot arm, also called an adjustable arc arm.

This mechanical change provided a significant benefit for sailors. Because the arc arm was faster than the screw worm drive, operators could work more quickly. They could measure multiple objects of different heights in a much shorter time. This was important for the fast-paced environment of naval warfare. The ability to switch between different heights quickly improved the speed of the entire measurement process.

The stadimeter remains relevant in modern naval operations. It is still used aboard United States Navy warships today. Even with modern technology, there are specific times when this optical tool is necessary. For example, sailors use it when using active radar is inadvisable. This shows how a tool designed in the late 19th century still serves a purpose in the modern age of technology.