Calibration means adjusting or fine-tuning a measuring instrument or device to ensure it provides accurate and precise results. It is like checking and setting a scale to make sure it measures weight correctly. Full definition
Furthermore, different model groups have different strategies for calibration of their simulations and that could cause some grouping. (realclimate.org)
The 1950 - 1960 data calibration period becomes a random occurrence. (climateaudit.org)
The adjustments are normal planned calibration for aging instruments and slight orbital drift. (judithcurry.com)