Usage examples "calculus":

If a cystic calculus
is present in the bladder it should be removed.  "Common Diseases of Farm Animals",
R. A. Craig, D. V. M..

Some years later, when his method of fluxions was published, another and a worse controversy arose this time with Leibnitz, who had also independently invented the differential calculus.
 "Pioneers of Science",
Oliver Lodge.

Nevertheless, this former conception of his, when compared to that wonderful complexity of ethereal lines, colors, tints and half tints which go to make up the modern New York girl, seemed inexpressibly simple, almost what plain arithmetic must appear to a man who has mastered calculus.
 "Tales From Two Hemispheres",
Hjalmar Hjorth Boysen.