The term work, defined in 1824 by French physicist Sadi Carnot, is the measure of the energy associated with the lifting of a weight through a gravitational height. [1] In human molecular interaction terms, i.e. with reference to human occupational work, the definition is the same, namely any activity energetically equivalent to lifting a weight. [2] The exact quantification of this measurement, e.g. when trying, for instance, to measure "household work" or "child raising work" as compared the work spent in lifting buckets of water up a well, is a major area of research in human thermodynamics. This is where the development of human indicator diagrams are needed.

The original indicator diagram, used to exactly quantify the work produced by a steam engine, was the 1796 indicator diagram, constructed by Scottish instrument maker James Watt and his employee John Southern, which was simply a chart of the pressure of the steam in a cylinder plotted out against the steam's volume:


From this, as was determined by French mining engineer Émile Clapeyron in 1834, the work of the steam can be determined using calculus:

References
1. (a) Quote: "we use here motive power (work) to express the useful effect that a motor is capable of producing. This effect can always be likened to the elevation of a weight to a certain height. It has, as we know, as a measure, the product of the weight multiplied by the height to which it is raised."
(b) Carnot, Sadi. (1824). “Reflections on the Motive Power of Fire and on Machines Fitted to Develop that Power.” Paris: Chez Bachelier, Libraire, Quai Des Augustins, No. 55.
2. Stoner, Clinton D. (2000). "Inquiries into the Nature of Free Energy and Entropy in Respect to Biochemical Thermodynamics." Entropy 2 [3], pgs. 106-141.