Chrono calibration: Mike at Skan tested our club one and sent it back with a certificate saying the maximum deviation from the true reading over ten shots, at various velocities up to 1000 fps.
Ours is within 2 feet per second of "true" at 1000 fps and closer than that at lower velocities.
I don't know what can be done to alter them but I guess that the clock speed is fixed by the crystal. That leaves the distance between the two sensors as about the only parameter that could be adjusted.
I imagine with rough handling it might be possible to jog a sensor out of position; the internal software relies upon that dimension as a given fixed amount, and if it is not as pre-programmed then the readings will all be in one direction, high or low.