The word just, in these phrases, is equivalent to “precisely.”
1881. Just what makes the best lodgement for oyster spawn intended to be used as seed, has been greatly discussed.—E. Ingersoll, ‘The Oyster-Industry,’ p. 96.
1884. Just how many bushels [of shells] a man will place in an acre depends upon both his means and his judgment.—Id., p. 95.
