The One who knows the details of each and every thing. The One who possesses all quantitative knowledge.
“On the Day that Allah will raise them all up (again) and show them the truth (and meaning) of their conduct. ALLAH HAS RECKONED ITS (VALUE),
though they may have forgotten it, for Allah is Witness to all things. Seest thou not that Allah doth know (all) that is in the heavens and on earth? There is not a secret consultation between three, but He makes the
fourth among them, nor between five but He makes the sixth, nor between fewer nor more, but He is with them, wheresoever they be: in the end will He tell them the truth of their conduct, on the Day of Judgment. For Al- lah has full knowledge of all things.”
(58:6-7)The Holy Quran
From the root h-s-y with the classical Arabic connotations: to number, count, reckon, compute to collect in an aggregate by numbering to register or record something to take an account of something to comprehend or know altogether to possess full comprehension.