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I want everyone to put on their thinking caps. This is about chronographs.

While doing some research about an Ontario gunsmith, I came across a letter written by Jack O'Connor about some cartridge tests using Vernon Speer's chronograph. I presume it was the company chrono. It was called the "Potter Counter Chronograph". This was probably made by the Potter Instrument Company.

Does anyone have any information about this chronograph and the company? It appears to be something that would have been used in the late 1940s into the 1950s. References to Potter Chronographs were made in various military documents of the time.