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Accurate Chronograph Measurements

By Joe Huffman
Copyright 2000

Summary of the Problem:

Being able to predict, with great accuracy, the flight path of your bullet depends upon having very accurate velocity information.  Given accurate information you can even calculate the BC of your bullets as fired in your gun.  It turns out that the raw, electronic, accuracy of the chronograph is a very minor concern compared to the variety of user errors that contribute to inaccurate data.  These errors need to be identified and corrected.  


The chronograph works via measuring the time between the detection of the shadow passing over two photo sensitive electronic devices.  These devices 'look' straight up and detect small changes in light intensity.  These devices are a known distance apart and if the time is known accurately the speed of the bullet can be determined.  If the photo sensor do not 'look' precisely straight up then the distance the bullet travels to cast it's shadow over the two sensors is different from the distance between the two sensors.  Figure 1 illustrates this.


Under construction.

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Email: Joe Huffman
Last updated: February 11, 2003