JDB, I've been chronographing for 35+ years now and gotta admit, I never lost any sleep over trying to "calibrate" a chronograph. I just follow the manufacturer's instructions in initial set up and all goes well. I have had no reason to distrust the manufacturer's factory calibration. They all seemed to give velocities that seemed reasonable to me for the load, barrel length, etc. being tested. If there is some anomaly in the results, I have found it most always related to sky conditions, not using the shades over the screens, etc. The problem quickly becomes apparent and I never tried to get into the electronics to recalibrate anything. Now once on a lark, a friend and I set up our chronographs in series, his an Oehler, mine a PACT. Velocities never varied more than one or two fps between the two. Close enough
for me...

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