"Careful calibration" means precisely adjusting or measuring something with great caution and attention to detail to achieve the desired outcome or accuracy. Full definition
But this technique is not perfect, and the beams require careful calibration using a flat, unchanging «reference surface.» (scientificamerican.com)
But with careful calibration we've been able to keep the fueling on, and just interrupt the ignition instead, halving the shift times.» (roadandtrack.com)
What you need to do is go back, do very careful calibrations, and write a paper about not finding anything so that it's useful. (discovermagazine.com)