Another variable that hasn’t been mentioned with the Shooting Chrony is the photodetector separation. Thus far, we’ve assumed that the separation is fixed, but inherent in the folding design is the hinges wearing over time. The sensor housings can shift slightly, as well. These factors can induce error in the readings. For a bullet travelling at a true speed of 3000 fps, and an assumed sensor separation of 1 ft, a 1/8” shift in the true sensor separation, whether due to wear and play in the hinges or to a shift of the sensor housings themselves, or both, is enough to cause an error of about 31 fps. Which amounts to about 1% of the measurement.
