Sentence:  The impact rate on 1958 Alpha for 153 events was * * f for particles of mass greater than * * f ( Dubin , 1960 ) ; this mass threshold was derived from the detector <WSD>calibration</WSD> and an assumed impact velocity of * * f . 
Meaning of the word marked with <WSD> tags:  the act of checking or adjusting (by comparison with a standard) the accuracy of a measuring instrument