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Old 01-05-2011, 11:44 PM
Unclenick Unclenick is offline
Join Date: Nov 2010
Posts: 1,067

The Boulangé chronograph is a 19th century electromechanical apparatus that uses a breakwire screen to open connections to solenoids. The first breakwire would cause a zinc rod to drop, while the second breakwire would release a spring-loaded striker that put a ding in the rod at whatever distance it had dropped to. Like its contemporary, the Bashforth chronograph, which traced a line on graph paper on a fast rotating drum during the interval between two wire breaks, this resulted in a graphical representation of time. Hence "chronograph" or literally "time drawing".

The modern direct reading bullet speed meters (what they really are) revived the use of the term, but not with the original meaning. The readout is a graph in the sense that writing is a graph, as in graphology. But it doesn't display time, so I think it's a poorly chosen term for the modern devices. Bullet speed meter just isn't sexy enough, I suppose, even if it's more accurately descriptive.

The early digital ballistic chronographs were built with vacuum tube logic for counting a crystal time base. The crystals were ultimately traceable to the old Bureau of Standards. I don't know the details of the proximity sensing coil system that was developed between the wars for use in place of breakwires as part of a portable system. I only know that, like the electromechanical devices from the 19th century, its response was slow. Without digital logic, the analog instruments need to make a big enough trace or meter movement to resolve small bits of time. That's why the first screen (wire or coil) was at 6 feet and the second was way out at 150 feet, for an average of 78 feet. That's where the military 78 foot rifle velocity measuring distance came from.

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Last edited by Unclenick; 07-13-2011 at 11:55 AM. Reason: typo fix
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