The word calibrate means making precise measurement. For example, you might want to calibrate your bathroom scale now and then to be sure it’s adjusted for exact weight. Or calibrate it to read five pounds light. We won't tell.
To find the origin of calibrate, we must look at its root, caliber, which appeared in the late 15th Century Middle French as calibre, meaning "a degree of importance." Linguists trace that word to an Arabic beginning, the word qalib, which referred to a mold for making bullets. That meaning seems to have carried over to our word, the verb calibrate, which first meant to measure the range of a projectile such as a bullet or shell.