Calx
Calx chalk (n.) Old English cealc “chalk, soft white limestone; lime, plaster; pebble,” a West Germanic borrowing from Latin calx (2) “limestone, lime (crushed limestone), small stone,” from Greek khalix “small pebble,”
calculus (n.) mathematical method of treating problems by the use of a system of algebraic notation, 1660s, from Latin calculus “reckoning, account,” originally “pebble used as a reckoning counter,” diminutive of calx (genitive calcis) “limestone” (see chalk).
felicific calculus A quasi-mathematical technique proposed by 19th-century utilitarian ethical theorists for determining the net amount of happiness, pleasure, or utility resulting from an action, sometimes regarded as a precursor of cost-benefit analysis.
The technique of felicific calculus was attributed to British philosopher Jeremy Bentham (1748-1832), described in chapter 4 of An Introduction to the Principles of Morals and Legislation (1789).